: How the 12 volt battery works on the Volt



silverton38
04-13-2012, 11:50 PM
I got this directly from an engineer at Chevrolet.

How is the 12v battery is charged?

The Volt does have a 12V battery, just like any other vehicle on the road. It is used the same way in the Volt as in other vehicles as well - that is to power electronics, computers, and accessories within the car. For example, things like radios, power windows, etc., are all powered off the 12V battery. It is only the propulsion battery & drive motors that are powered by the high voltage battery. The 12V battery is actually not used to start the engine/generator the vehicle uses the high voltage battery to do this.


When do you know if the 12V battery is dead?

Just like any vehicle, you would know if the 12V battery is dead because nothing would work. Things like power locks, windows, radios, etc., would not function. Although we do not use the 12V battery to start the gasoline generator, it cannot be started either, because all of the computer & control systems in the car are powered from the 12V battery, so if they cannot be powered, then the engine cannot be started.

Does it charge while the vehicle is moving?

Not in the sense that vehicle motion puts energy into the 12V battery, but yes, the 12V battery is charged whenever the car is "on". Again, it helps to compare to a gasoline vehicle here. In a gasoline vehicle, the battery is charged when the engine is running (by the alternator). In the Volt, whenever the vehicle is "running" (i.e. powered on), the 12V battery is being charged, although not by an alternator, but rather by a converter that takes power from the high voltage battery.

If I leave my volt plugged in and leave my lights on will it drain the 12v ?

This depends on whether the car is "on" or not. Again, think of a gasoline car. If you leave it parked, with the engine off, and the lights on, then your 12V battery will be drained. If you leave the engine running, then you will not drain the 12V battery (as the engine will keep it charged). Same is true in a Volt. If the car is "powered off" and you leave the lights on, this will drain the battery. If the car is "powered on" then the battery will be kept charged.

Does the 12 volt slave off of the home charger if needed?

No, it does not. The charger that charges the 16kWh traction battery converts 120V AC or 240V AC into high-voltage DC to charge the Lithium Ion propulsion battery. There is a separate module in the car that charges the 12V battery. This "Accessory Power Module" converts high-voltage DC (from the 16kWh battery) into 12V DC (for the 12V battery). This module is only "turned on" when the car is "running" or powered on. (again, think, just like an alternator in a gasoline vehicle - it is only "on" and producing power when the car is running).

Nrsk4u
04-14-2012, 12:28 AM
That's interesting, I wonder how much further I could go on the main battery if I turn the radio and daytime running lights off....

mikeg3
04-14-2012, 06:23 AM
One role the 12V battery plays is that no Volt functions, even the power door lock, will operate in a powered off Volt with a fully charged main battery and a discharged 12V battery. Once the Volt is turned on, the main battery supplies power to all Volt systems with no help needed from the 12V battery. The computers, etc., are powered by the 12V bus which is supplied both by the 12V battery and by the Accessory Power Module powered by the main battery.

I found my 12V battery dead one morning while the Volt was still 240V plugged in. The moment 12V was applied to the jumper terminals under the hood, the Volt started and ran normally. The main battery was fully charged, which one would expect since it was 240V plugged in all night. The dealer found no problems except a drained 12V battery.

If the Accessory Power Module is on whenever the Volt is on, then leaving the Volt on and plugged in should never fully discharge the 12V battery.

WOT's theory was that we had left our Volt on all night and drained the 12V battery.

Is silverton38's Chevy engineer wrong or is WOT wrong?

bonaire
04-14-2012, 08:54 AM
>> In the Volt, whenever the vehicle is "running" (i.e. powered on), the 12V battery is being charged, although not by an alternator, but rather by a converter that takes power from the high voltage battery.
<<

It seems that with the number of 12V batteries that have been reported going dead over the last year or so, some type of sensible feature should be enabled such that the Volt could turn on this secondary DC power converter to charge the 12V even when plugged into the wall. This is one power management area that may have not been fully engineered to guard against dead 12V's. Yes, you can jump start it with a simple jump-start kit or 2nd battery. But with a full traction battery, having the 12V go dead and leaving you stranded has always sounded a bit limiting whenever someone posts about it.

If you're into the RC hobby, A small 12V LiFePO4 RC-grade pack could be kept around at home or in the car in case it goes dead. You'd think a 4Ah 13V 4-cell pack could be a simple jump-pack. I don't suggest a Li-Poly pack due to its issues with heat and volatility. Of course, there are the consumer-grade jump packs available too which are charged by plugging into the wall. I only suggest the packs above if you know what you're doing with them, otherwise call the auto-service or do a regular car-to-car jump.

WopOnTour
04-14-2012, 01:15 PM
I got this directly from an engineer at Chevrolet.

.Your "Chevy Engineer" has it wrong on a few counts actually (Even if he/she actually is an engineer with GM it's doubtful they have much to do with the Volt IMO)

Q: Does the 12 volt slave off of the home charger if needed?
WOT's A: Actually yes it does (well sort of, but remember the charger is in the car, not in your home). So despite what your Chevy Engineer says, the 12V does actually get an auxillary charge when OFF and plugged in but only while charging is actively taking place.(i.e. steady "ON" green LED on dash)

However charging current DOES NOT come from the DC-DC converter as it normally would when the car is "ON". Instead it comes from a totally separate 12V charger that is built directly into the on-board charging module. So as long as your car is actually charging the Lithium Ion battery (again, steady green LED) then so too is your 12V battery. This is necessary because there needs to be a certain number of 12V modules and devices electrically participating during charging operations and it doesnt really make sense to draw current FROM the Li-Ion source when our primary goal is to charge it, and since the DC-DC converter is only ON when the car is ON, there is a neccesity for this auxillary 12V charger.

Q: If I leave my volt plugged in and leave my lights on will it drain the 12v ?
WOT's A: It's pretty obvious that the 12V battery won't just immediately go dead if the car is on isn’t it? (more on that scenario in a bit) But I'm pretty certain the question was being posed assuming the car was turned OFF and someone had “left their lights on”. (assuming I guess they had been manually turned ON while driving as opposed to using the AUTO feature)
The Volt, like most GM cars actually, is equipped with a battery run-down feature. If you had inadvertently left your lights on (including a map light or other interior light) the system is designed to automatically turn OFF these lamps after approximately 20 minutes. Since a single module (the BCM) is “in charge” of ALL of your interior or exterior lighting this feature is easily accomplished by the ability to detect the switch inputs and software driven timers (Note: in some documentation it will say 10 minutes which is technically true but doesn’t include the potential for 10 minutes in Retained Accessory Power mode or re-entry into another temporary power mode after plugging in )

Now there are a few caveats to this anti-rundown operation as it techncially CAN be manually overridden by turning any switch left ON, to OFF then back ON again. This is a manual override that would indicate to the system you need your light/s on for some emergency purpose and in this case, the lamps will stay ON until the 12V battery is depleted. I suspect a few people have actually been “caught” by accidentally going into this over-ride mode.

As far as your 12V battery not ever being run down while the Volt is "On" that of course depends on how long it will take for the Li-Ion battery to reach a critically low state of charge after it runs out of fuel. (basically do different than of running out of gas idling on a conventional car) It won't be able start the engine in this event, so instead the HV system "load sheds" (to protect the Li-Ion battery from going too deep) and when it hits the hard floor ~15% SOC all DC-DC conversion also ceases (the last load to shed) and since the power mode is still "ON" everything in the car is being powered by the 12V battery eventually it will be dead as a door nail.

HTH
WopOnTour

Jim Fallston Md.
04-14-2012, 01:31 PM
This is from the owners manual page 6-6.

Battery Power Protection

The battery saver feature is designed to protect the vehicle's 12‐volt battery. If the exterior lamps or any interior
lamp is left on and the vehicle is turned off, the battery rundown protection system automatically turns the lamps off after about
10 minutes.

So in theory if you leave any of the lights on it will not drain the 12 volt battery. This has been a feature on all GM vehicles since they started adding auto headlamps if I remember correctly.

mikeg3
04-14-2012, 01:46 PM
As far as your 12V battery not ever being run down while the Volt is "On" that of course depends on how long it will take for the Li-Ion battery to reach a critically low state of charge. (basically the equivalent of running out of gas idling on a conventional car) It won't start the engine in this event. Instead the system "load sheds" (to protect the Li-Ion battery from going too deep) and DC-DC conversion ceases andsince the power mode is still "ON" everything is being powered by the 12V battery eventually it will be dead as a door nail.

HTH
WopOnTour

This doesn't explain how a Volt's 12V battery can be completely discharged in 12 hours when the main battery is fully charged and connected to the 240V charger (these two facts I guarantee) while the car is on (your theory, not mine).

BTW, our headlight switch is always on AUTO.

WopOnTour
04-14-2012, 01:47 PM
This is from the owners manual page 6-6.

Battery Power Protection

The battery saver feature is designed to protect the vehicle's 12‐volt battery. If the exterior lamps or any interior
lamp is left on and the vehicle is turned off, the battery rundown protection system automatically turns the lamps off after about
10 minutes.

So in theory if you leave any of the lights on it will not drain the 12 volt battery. This has been a feature on all GM vehicles since they started adding auto headlamps if I remember correctly.Yes techncially it IS 10 minutes, but that particular timer won't start until the vehicle power mode OFF status is transmitted across the GM-LAN bus to other modules on the network. There can be numerous conditions that may delay this event (up to 10 min) so I always just say 20 minutes in order to be safe...
HTH
WOT

scottf200
04-14-2012, 04:16 PM
<snip>Yes, you can jump start it with a simple jump-start kit or 2nd battery. But with a full traction battery, having the 12V go dead and leaving you stranded has always sounded a bit limiting whenever someone posts about it.

If you're into the RC hobby, A small 12V LiFePO4 RC-grade pack could be kept around at home or in the car in case it goes dead. You'd think a 4Ah 13V 4-cell pack could be a simple jump-pack. I don't suggest a Li-Poly pack due to its issues with heat and volatility. Of course, there are the consumer-grade jump packs available too which are charged by plugging into the wall. I only suggest the packs above if you know what you're doing with them, otherwise call the auto-service or do a regular car-to-car jump.

See post here on a $27 option that does just that (jump car from lighter/accessory power plug):
http://gm-volt.com/forum/showthread.php?12987-PLEASE-HELP!-2012-Volt-will-not-power-on-start.-PLEASE-HELP!&p=138715#post138715

scottf200
04-14-2012, 04:19 PM
From FAQ in my sig:

All about the 12V accessory battery, including how it stays charged, and jump starting the Volt
http://gm-volt.com/forum/showthread.php?5409-Auxillary-Battery&p=44692#post44692

silverton38
04-14-2012, 07:59 PM
I asked Chevrolet specifically for an answer to these questions and they sent it to Volt Engineering and this is the reply. They knew that it would be posted.

I would agree that the 12 volt battery should be charged with the car but it is not. It is charged while the car is operational. Since the generator starter uses the main battery; I do not think they should even have a 12 volt battery (personal belief).


Regardless; we all need to know how this battery works so that we can manage it. It would be fun boosting an electric car :)

WopOnTour
04-14-2012, 10:02 PM
I asked Chevrolet specifically for an answer to these questions and they sent it to Volt Engineering and this is the reply. They knew that it would be posted.

I would agree that the 12 volt battery should be charged with the car but it is not. It is charged while the car is operational. Since the generator starter uses the main battery; I do not think they should even have a 12 volt battery (personal belief).


Regardless; we all need to know how this battery works so that we can manage it. It would be fun boosting an electric car :)Again, I repeat. This is incorrect.
Either they were simply mistaken OR you are interpreting/transposing their response incorrectly.

Don't believe me or want to prove me wrong? No problem
Try this.
Put even a basic $10 Radio Shack voltmeter across your + and - battery posts. (to access them lift off the small square black plastic covers in your rear hatch storage area)
Then once you have a reading (say ~12-13V) then plug in your Volt and read/record the voltmeter again a few seconds after the green LED comes ON steady.It will increase above your initial reading to indicate charging is taking place.

There is very good reasons why we still require a 12V battery. Yes, the lithium ion battery is used to start the ICE once the initial charge is depleted but that will only occur once you achieve the minimum speed for CS. Up until that point the car had been operating electrically and it is the 12V management system that permits the high-voltage an electrical pathway to the traction motor.

As a new volt owner and member I suggest you start by reading up in the FAQs in the Newcomers forum on this site (http://gm-volt.com/forum/showthread.php?5801-Frequently-Asked-Questions&p=47963#post47963) for more information.

Welcome to gm-volt.com

HTH
WOT

vdiv
04-14-2012, 11:00 PM
So while the propulsion 380 V battery is being charged, the auxiliary 12 V battery is also being charged. What happens when the propulsion battery is fully charged and the car remains plugged in? Can the auxiliary battery in this case be completely discharged or is the charge on it also being maintained? Do we need to carry jumper cables/jumper batteries in the Volt if we leave it plugged in at say the airport for a month?

DonC
04-15-2012, 12:27 AM
Do we need to carry jumper cables/jumper batteries in the Volt if we leave it plugged in at say the airport for a month?It's going to be like any car. If you're comfortable leaving your ICE the Volt isn't going to be that different, though it has a lot of electronics which can be potential drains. I always carry jumpter cables. Scott's little charger is a good idea. WOT suggested a mod where you apply clips in case the BCM is dead.

Maybe WOT or someone else can help me out? I'm wondering why the manual says to jump to the front connectors. Most times it would be more convenient to jump from the back since in parking lots you usually pull in head first and there may not be a space available next to you. Perhaps using the front connectors protects the accessories since there is a lower amp fuse or something? Anyway carrying the Wagan battery booster and using the rear connectors would seem to be a piece of cake.

mikeg3
04-15-2012, 01:59 AM
If the 12V battery is dead you can't easily open the trunk.

You can open the front door and then the hood mechanically. Once 12V is applied to the jumper terminals, you can immediately start the car and then the main battery though the DC-DC converter starts supplying 12V to the car and also charging the 12V battery.

My question, which others have also asked above, is whether or not the 12V battery is being charged by the On Board Charge Module or the DC-DC converter when the vehicle is off, the 110V/240V charger is plugged in, and the main battery is at maximum charge. This would explain how a plugged in Volt can go dead.

volt3939
04-15-2012, 02:17 AM
If the 12V battery is dead you can't easily open the trunk.

You can open the front door and then the hood mechanically. Once 12V is applied to the jumper terminals, you can immediately start the car and then the main battery though the DC-DC converter starts supplying 12V to the car and also charging the 12V battery.

My question, which others have also asked above, is whether or not the 12V battery is being charged by the On Board Charge Module or the DC-DC converter when the vehicle is off, the 110V/240V charger is plugged in, and the main battery is at maximum charge. This would explain how a plugged in Volt can go dead.

Good point about the trunk.

Your question has already been answered:


...

Q: Does the 12 volt slave off of the home charger if needed?
WOT's A:...

the 12V does actually get an auxiliary charge when OFF and plugged in but only while charging is actively taking place.(i.e. steady "ON" green LED on dash)

However charging current DOES NOT come from the DC-DC converter as it normally would when the car is "ON". Instead it comes from a totally separate 12V charger that is built directly into the on-board charging module. So as long as your car is actually charging the Lithium Ion battery (again, steady green LED) then so too is your 12V battery. This is necessary because there needs to be a certain number of 12V modules and devices electrically participating during charging operations and it doesn't really make sense to draw current FROM the Li-Ion source when our primary goal is to charge it, and since the DC-DC converter is only ON when the car is ON, there is a necessity for this auxiliary 12V charger.
...
WopOnTour

Emphasis mine...

WopOnTour
04-15-2012, 03:23 AM
It's going to be like any car. If you're comfortable leaving your ICE the Volt isn't going to be that different, though it has a lot of electronics which can be potential drains. I always carry jumpter cables. Scott's little charger is a good idea. WOT suggested a mod where you apply clips in case the BCM is dead.

Maybe WOT or someone else can help me out? I'm wondering why the manual says to jump to the front connectors. Most times it would be more convenient to jump from the back since in parking lots you usually pull in head first and there may not be a space available next to you. Perhaps using the front connectors protects the accessories since there is a lower amp fuse or something? Anyway carrying the Wagan battery booster and using the rear connectors would seem to be a piece of cake.As per the owners manual under "jump starting" underhood boost points are to be used for a Volt to accept a boost/jump from another vehicle, but becuase the + boost point IS fuse protected (80A) these points MUST NOT to provide a jump to another vehicle. (in that case connect the cables directly at the 12V battery in the rear of the car)

mikeg3 is correct, one of the primary considerations for this is the fact that the rear hatch area may not be accessible when the 12V battery is dead as the latch release it electrically operated.
However in an emergency the rear hatch CAN be released mehanically from teh inside.(after folding down teh rear seats of course) If you look on the inside edge of the hatch just below the glass, there is a small rectangular plastic cap/plug that can be removed with a small flat-bladed screwdriver or other tool. You then must insert a blade-type screwdriver vertically into the hole to engage the lever and turn counter-clockwise to release the latch. I beleive Rusty may have even posted some pics of the proces, see the Volt FAQs (http://gm-volt.com/forum/showthread.php?5801-Frequently-Asked-Questions) for more info.

and YES, since the 12V battery is being only charged while in the act of charging the Li Ion battery, if charging stops for ANY reason (including having reached a full charge) then 12V charging ceases at that point as well.

WopOnTour

mikeg3
04-16-2012, 05:14 PM
I was looking at ChevroletVoltage.com and found an interesting comment. As background, WOT said, and I confirmed by taking a magnifying glass to page 100 of the SAE Volt compendium, that the On Board Charging Module takes power from the 110V or 240V charger and feeds the main battery and separately feeds the 12V battery. But at some point the main battery is full and the On Board Charging Module no longer has a power source. What can happen then to the 12V battery if the car is left on or the car is left plugged in for weeks?

BobGPSr's salesman: "Okay, talked to the resident Volt expert technicians. They had instant answers to your questions. Your 2012 Volt does charge and maintain the 12 volt battery as long as it is plugged in. Apparently GM listened and changed that since the blog posts that you found. ..."

Is this correct? Is the change available for 2011 Volts? What's the technical bulletin number?

silverton38's sources sound both accurate and authoritative, but I don't know. Here is his full thread:
http://www.chevroletvoltage.com/index.php/community.html?func=view&catid=11&id=6271

This would mean that some other module, like the Auxiliary Power Module or the DC-DC voltage step-down converter (same thing?) will trickle charge the 12V battery from the fully charged main battery after the On Board Charging Module is no longer getting power from the external charger.

Henry_FL
04-16-2012, 06:27 PM
I went out to my volt, which is fully charged and has a kill-o-watt connected so I can see the power drain.

Turned on the lights headlights for 5 minutes, charger never kicked on as measured by the amp draw using the kill-o-watt, so this is counter to what you posted

mikeg3
04-16-2012, 06:45 PM
Henry_FL: The quote said that there was a "change". Perhaps you and I just don't have the change installed.

Henry_FL
04-16-2012, 07:08 PM
Mine a recent VIN and there are no software updates my vehicle is missing ( that I have read about anyways )

DonC
04-16-2012, 08:13 PM
I doubt there is a difference between the 2011 and 2012 models. My guess would be both have a 12v charger which charges the 12v battery when the Volt is plugged in and charging. The DC-DC charging only occurs when the car is powered "on". This is more or less what the OP said except they didn't mention the 12v charger.

vdiv
04-16-2012, 08:17 PM
It would be an astonishing omission to have the Volt plugged in with the propulsion battery fully charged, and have the auxiliary battery discharge and unable to power the electronics to unlock or start the car, especially if the car already has a dedicated auxiliary charger in place. In such a case indeed it would be great to have that fixed. Maintaining the auxiliary battery charge does not use much power.

mikeg3
04-16-2012, 08:56 PM
It would be an astonishing omission to have the Volt plugged in with the propulsion battery fully charged, and have the auxiliary battery discharge and unable to power the electronics to unlock or start the car

I agree with you but I can assure you that this happened to me.

Remember that when the main battery is fully charged, the 110V/240V charger stops providing power to both batteries.

There are then two questions:

The Volt can be plugged in or not, but that should make no difference since the charger is stopped.

The Volt can be on or off. But that shouldn't matter - there is a lot going on electronically when the Volt is off.

Bob_Livonia
04-16-2012, 09:11 PM
There is a contactor on the high voltage battery, which is disconnected for safety when the vehicle is not charging or running. The accessory power module charges the 12 volt battery by stepping down the high-voltage battery's power. So I would be very surprised, even on the 2012's if the 12V battery charges when the contactor is open. I remember a GM Techline article warning dealers the 12V battery can discharge even when the charge cord is plugged in. It seems there would be duplication, or else clever circuitry needed to allow the AC power input to charge the 12V battery when the contactors are open.

Cord
04-16-2012, 09:16 PM
It really depends on where the smarts are for the Chevy volt idea of a voltage regulator. If the car computer needs to be running to charge and trickle charge the 12 volt battery then even if the car is plug in the 12 volt battery could go flat.

I use a 12 volt monitor in the car and see at least 2 and possibly a third. Voltages on the battery
12.5 and 14.7 volts . I only. See this when driving as the meter is in the power port and they turn off after a delay when shutting down the car.

We could test if outside events puts power into the 12 volt battery.
Remote start
Outside temperature ie too hot or cold and the car reacts to protect the main battery.

The volt does needed a volt meter. I still can not tell if there is engine code to onstar for a low 12 volt battery or a dash ligh follow battery.

I keep a 8 cell pack of D batteries in car just in case.

We should connect the 2 other older threads on the 12 volt battery charging discussion.

mikeg3
04-16-2012, 10:19 PM
There is a contactor on the high voltage battery, which is disconnected for safety when the vehicle is not charging or running. The accessory power module charges the 12 volt battery by stepping down the high-voltage battery's power. So I would be very surprised, even on the 2012's if the 12V battery charges when the contactor is open. I remember a GM Techline article warning dealers the 12V battery can discharge even when the charge cord is plugged in. It seems there would be duplication, or else clever circuitry needed to allow the AC power input to charge the 12V battery when the contactors are open.

OK, that covers the case where the car is off and the main battery is fully charged.

What about the case where the car was left on and the main battery reaches full charge. Why would the contactor open? Why would the 12V battery fully discharge overnight?

Just as background, I went down one morning and my Volt was totally dead. The Volt was plugged in to 240V. Applying 12V to the jumper terminals let me start the car. The main battery read fully charged. GM thinks that we left the car on overnight. I don't see how parking the car plugged in and turned on is worse than parking the car unplugged and turned on or driving the car unplugged and turned on.

Does the contactor open when the car is in Park but turned on?

I just don't get it.

BobGPSr
04-16-2012, 11:59 PM
Why is this such a big secret?

Why can't GM just answer with clear unambiguous authority that the current 2012 Volt will maintain the 12 volt battery charge indefinitely as long as it is plugged into a level 1 or level 2 charger?

This answer needs to be put to rest immediately!

mikeg3
04-17-2012, 12:59 AM
Why is this such a big secret?

Why can't GM just answer with clear unambiguous authority that the current 2012 Volt will maintain the 12 volt battery charge indefinitely as long as it is plugged into a level 1 or level 2 charger?

This answer needs to be put to rest immediately!

I can answer half of your question by referring to my experience and to previous posts in this thread by Henry_FL and Bob Livonia. There are times when the Volt is physically plugged in, the main battery is fully charged, and the 12V battery is not trickle charged and can run down.

Here is a quote from the June 2011 GM Tech Link:

Volt 12V Battery Charging
By Blog Post on June 1, 2011 9:59 PM | No Comments
The Volt is equipped with a 12 volt battery just like all conventional vehicles. When displaying the vehicle, such as in the new car showroom, there is a common misconception that having the charge cord plugged in will maintain the 12 volt battery (either with the stationary 240V or portable 120V charger).

With the charge cord plugged in, the vehicle will charge the 300V battery and will also maintain the 12 volt battery to power up the modules needed to complete the charge event. When the 300V battery is fully charged, the modules will go to sleep and the vehicle will no longer trickle charge the 12 volt battery even though the charge cord is still plugged in.

If the vehicle is in Service Mode (by holding the Power button for 7-8 seconds without pressing on the brake pedal), all modules on the vehicle will stay awake, but the charging system will not be charging the 12 volt battery. This is the same as leaving the key in the On position (with the engine off) on a conventional vehicle.

TIP: The ignition should not be left in the Service Mode for more than five minutes without having a battery maintainer attached to the 12 volt battery.

To properly maintain the 12 volt battery while displaying the vehicle, use a battery maintainer, such as the EL-49642. The charge voltage should be kept below 14.8 volts due to the Volt having an AGM battery.

Periodically driving the vehicle also will activate the Accessory Power Module (APM) and can help to maintain and charge the 12 volt battery.

- Thanks to Ashmi Haria


Notice the reference to driving the Volt activating the Accessory Power Module. So it's not enough for the Volt to be powered on.

We would appreciate some clarity as to when the 12V battery will be trickle charged and when it will not.

BobGPSr
04-17-2012, 01:06 AM
Please give us a very very clear answer, GM!

DonC
04-17-2012, 01:27 AM
It seems pretty straightforward. The 12v will be charged if the 300v battery is being charged or if the car is powered on. I suspect the reference to driving was inadvertent.

mikeg3
04-17-2012, 01:43 AM
It seems pretty straightforward. The 12v will be charged if the 300v battery is being charged or if the car is powered on. I suspect the reference to driving was inadvertent.
If that is correct, WOT and my Volt Adviser were wrong. They believe a powered on Volt will not maintain the 12V battery charge if you accidentally leave the car on overnight, even with a fully charged main battery and a plugged in charger.

I know for a fact that my Volt was plugged in, fully charged, and had a dead 12V battery in the morning. If the car was off, why was the 12V battery dead? If the car was on, why was the 12V battery dead? And we did not use Bluetooth that night.

Is the Auxiliary Power Module on whenever the Volt is on and the main battery has a good SOC?

BTW, I tried everything to get the relevant microprocessor logs dumped, but no one thought the situation warranted it.

DonC
04-17-2012, 02:36 AM
If that is correct, WOT and my Volt Adviser were wrong. They believe a powered on Volt will not maintain the 12V battery charge if you accidentally leave the car on overnight, even with a fully charged main battery and a plugged in charger.I don't understand how you're reaching this conclusion from what WOT wrote, which was that:

As far as your 12V battery not ever being run down while the Volt is "On" that of course depends on how long it will take for the Li-Ion battery to reach a critically low state of charge. (basically the equivalent of running out of gas idling on a conventional car) It won't start the engine in this event. Instead the system "load sheds" (to protect the Li-Ion battery from going too deep) and DC-DC conversion ceases andsince the power mode is still "ON" everything is being powered by the 12V battery eventually it will be dead as a door nail.

I'm not sure how he could be more clear that so long as the Volt is "ON" the lager battery pack will charge the 12v battery until it runs out of charge.

mikeg3
04-17-2012, 07:57 AM
I don't understand how you're reaching this conclusion from what WOT wrote, which was that:

As far as your 12V battery not ever being run down while the Volt is "On" that of course depends on how long it will take for the Li-Ion battery to reach a critically low state of charge. (basically the equivalent of running out of gas idling on a conventional car) It won't start the engine in this event. Instead the system "load sheds" (to protect the Li-Ion battery from going too deep) and DC-DC conversion ceases andsince the power mode is still "ON" everything is being powered by the 12V battery eventually it will be dead as a door nail.

I'm not sure how he could be more clear that so long as the Volt is "ON" the lager battery pack will charge the 12v battery until it runs out of charge.

The main battery won't get critically low while plugged in. The Volt will just enable input from the charging station.

My car was definitely plugged in while the 12V battery ran down. So was Ashni Haria's battery in the GM Tech Link article, except my car was on in normal mode and his car was on in service mode.

BTW, I haven't done the math, but I think it would take quite a long time for a CAN plus headlights to discharge 10 KWH. The Volt was parked the whole time.

Bob_Livonia
04-17-2012, 08:43 AM
Read Maynard's thread about long-term storage and the need for a trickle charger (as opposed to just leaving the charge cord plugged in):
http://gm-volt.com/forum/showthread.php?13160

The 12 volt battery is charged from the high voltage battery through a DC-DC converter (accessory power module) and by no other means. So it comes down to under what conditions the contactor is closed. The contactor is open, for safety reasons, when energy to or from the HV battery is not needed .

As far as running down the 12V battery, there are plenty of ways to do that, especially considering its small size (it does not need to power a starter). Leaving the car in service mode (hold the start button 7 seconds with foot off the brake) will do it; leaving data logging equipment connected that keeps the data bus up will do it; plus there are almost an infinite number of fault conditions which can cause 12V battery draws resulting in a dead (12V) battery, just like in any other car.

mikeg3
04-17-2012, 09:16 AM
Look at Khwaja Rahman's 4/12/2001 paper "The Voltec 4ET40 Electric Drive System" found in the SAE hardcover Volt compendium. Figure 1 shows a separate path from the On Board Charge Module to the 12V battery. However, that will only be live when the Volt is plugged in and the main battery is not fully charged. This agrees with WOT.

The issue is what other ways the 12V battery can be charged. You say that depends on the main battery's contactor, since when the contactor is open the Auxiliary Power Module can't get power. Is the contactor always open when the Volt is in Park?

However, Roland Mathe's 4/12/2011 paper "VOLTEC Battery System for Electric Vehicle with Extended Range" in the same book says that there are five contactors that open and close independently as needed. The APM has it's own contactor. Why doesn't that contactor close as needed to allow the APM to charge the 12V battery? This question applies separately to when the car power is on and when the Volt is powered off.

I would include the text, but the book came with a separate strict copyright warning. I think this comes under fair use, but SAE needs the money.

DonC
04-17-2012, 10:02 AM
My car was definitely plugged in while the 12V battery ran down. So was Ashni Haria's battery in the GM Tech Link article, except my car was on in normal mode and his car was on in service mode.I have no idea about what happens if the car is plugged in and powered on. Normally we talk about having the car unplugged when powered on. Out of curiosity, why did you have it plugged in and powered up?

The combination of powered on and plugged in would be sui generis. It's a twilight situation where the central issue would be what the person intended to do next, turn the power off and charge or unplug the EVSE and drive. Lots of special conditions apply, one of which is that for safety reasons you can't move out of park. For purposes of charging the battery this may be the same as "Service Mode".

Bob_Livonia
04-17-2012, 10:25 AM
Look at Khwaja Rahman's 4/12/2001 paper "The Voltec 4ET40 Electric Drive System" found in the SAE hardcover Volt compendium.

The issue is what other ways the 12V battery can be charged. You say that depends on the main battery's contactor, since when the contactor is open the Auxiliary Power Module can't get power. Is the contactor always open when the Volt is in Park?

I think you mean 2011, not 2001.

I will defer to the experts on the contactors; I know there are multiple contactors. But you never want the HV battery to discharge below the calibrated limit, because this prevents "bricking" of the battery as alleged has happened on the Tesla - I'd prefer a jump start and perhaps replacing the small 12V battery than risk damaging the lithium ion battery any day.

mikeg3
04-17-2012, 11:15 AM
I have no idea about what happens if the car is plugged in and powered on. Normally we talk about having the car unplugged when powered on. Out of curiosity, why did you have it plugged in and powered up?

The combination of powered on and plugged in would be sui generis. It's a twilight situation where the central issue would be what the person intended to do next, turn the power off and charge or unplug the EVSE and drive. Lots of special conditions apply, one of which is that for safety reasons you can't move out of park. For purposes of charging the battery this may be the same as "Service Mode".

If you're going to use big words, I'm telling the teacher. :)

Two situations that make a plugged in, turned on, parked Volt less sui generis are the driver who plugs in his car for the night but forgets to turn the Volt off (this and Bluetooth are the two official GM explanations for a dead 12V battery) and the dealer who leaves the car on the showroom floor and turned on and plugged in to show off the fancy display to browsing customers (see Ashmi Haria's GM Tech Link article above). It would also be a good way to store a locked car for a month or two in a protected environment. Please tell us exactly what happens in the battery fully charged, car turned on and plugged in, shift in Park situation.

Your other post about protecting a low SOC main battery deals with a different situation. A plugged in Volt with a low SOC will be drawing power from the charger and the On Board Charge Module separately charges the 12V battery. No issue there.

BTW, in service mode, the engines are disengaged while all the electronics are live. I think that the contactor between the main battery and the inverter is open. Ashmi wanted to run this way, perhaps to be sure that the ICE never started indoors.

WopOnTour
04-17-2012, 12:32 PM
I can answer half of your question by referring to my experience and to previous posts in this thread by Henry_FL and Bob Livonia. There are times when the Volt is physically plugged in, the main battery is fully charged, and the 12V battery is not trickle charged and can run down.

Here is a quote from the June 2011 GM Tech Link:


Notice the reference to driving the Volt activating the Accessory Power Module. So it's not enough for the Volt to be powered on.

We would appreciate some clarity as to when the 12V battery will be trickle charged and when it will not.You're making a mountain out of a mole hill. There really doesn't need to be multiple threads debating the exact same topic. (so I've merged it)

The TechLink article is pretty clear and mirrors what we here at gm-volt.com have been repeatingly telling you in the other threads.
But you don't need to drive the car to engage the Auxiallary Power/14 Volt Power Module (yes, the DC-DC converter) merely step on the brake and press the power button.I realize the article appears to allude that you need to drive the car but techncially the "drive cycle" commences when you power up the Volt intending to drive it. Just as you do when you turn the key to START a regular car, while your not "moving" you are still "driving" (and "charging" at that point as well for that matter)

I suggest you buy or borrow a voltmeter and in a matter of minutes satisfy yourself when the 12V battery does and does not charge. I am certain it will emulate exactly what has been explained to you here in this thread.

Then "Just Drive and Smile"...
WopOnTour

scottf200
04-21-2012, 07:32 PM
I got a little confused because I think threads were merged and the flow was off. I saw references to Ashmi Haria's input but not quotes or a link. See red.


Why is this such a big secret?
Why can't GM just answer with clear unambiguous authority that the current 2012 Volt will maintain the 12 volt battery charge indefinitely as long as it is plugged into a level 1 or level 2 charger?
This answer needs to be put to rest immediately!


I remember a GM Techline article warning dealers the 12V battery can discharge even when the charge cord is plugged in.

http://www.archivedsites.com/techlink/2011/11/volt-12v-agm-battery-testing-1.html

Volt 12V AGM Battery Testing
By Blog Post on November 1, 2011 7:05 PM
<snip>

For information on how to properly maintain the Volt's 12V battery in dealership showrooms, review #PIC5448. There is a common misconception that having the charger plugged in will maintain the 12V battery (either with the stationary 240V or 120V charger).

When plugging in a 240V or 120V charger, the vehicle will charge the 300V battery and will also maintain the 12V battery to power up the modules needed to complete the charge event. When the 300V battery is fully charged, the modules will go to sleep and the vehicle will no longer trickle charge the 12V battery even though the 240V or 120V charger is still plugged in.
- Thanks to Ashmi Haria

BobGPSr
04-24-2012, 04:02 PM
Chevy blew it on the Requirements Analysis. Having the Volt die due to a flat battery is NOT ACCEPTABLE when the car is plugged into a charger.

WopOnTour
04-24-2012, 07:29 PM
Chevy blew it on the Requirements Analysis. Having the Volt die due to a flat battery is NOT ACCEPTABLE when the car is plugged into a charger.I still think there's something you're missing here.
It would take months for a "flat" 12V battery to occur at normal OFF levels of parasitic drain on the Volt (~10mA)
So not much different than any other modern car.

I mean assuming when plug-in charging STOPS both the high voltage and 12V batteries will be fully charged. (and you dont want to overcharge them)
So what's the problem?

Did you have something go wrong with your Volt BobGPSr??

WopOnTour

BobGPSr
04-25-2012, 12:50 AM
I have not yet had a problem with the 12 volt battery in my Volt.

I am astonished about the warnings posted here about GM manuals warning dealers about the 12 volt battery being discharged on a show room floor. How different is that from coming back from a three week trip and finding the Volt inoperable due to the 12 volt battery being discharged even though the Volt was left plugged into a good working charger? Why the instructions from GM about external trickle charging the 12 volt battery if there is a issue with overcharging it? It is my understanding that the technology used in the 12 volt battery permits indefinite trickle charging. Do you, WopOnTour, know for a fact that this is not so?

I am fully capable of rigging a low current trickle charger for the 12 volt battery for my home garaged Volt when I plan on not using it for a few weeks. But this should not be necessary when the Volt is already plugged into a level 1 or level 2 charger and I am disappointed if it is necessary.

Maybe just doing a remote start, but from reading the manual that is only good for two 10 minute periods between normal Starts. Seems that programming a computer to do this using OnStar could be done -- but then why doesn't the Volt have its computers do this? Just a bit of monitoring the voltage of the 12 volt battery and "Start"ing the car for a 12 volt battery recharge as necessary.

Cord
04-25-2012, 04:32 AM
Because dealers tend to forget and leave the car in accessory mode or customer pushed the start button for 6 sec. Playing around with the parking break puts a load on the battery when the car is off.

"indefinite trickle charging" that's a wide open statement. But a smart charger still should have a cut off voltage.

I have a 12 volt meter on my dash and eight D-cell primary batteries with crocodile clips in the glove box just in case.

After read all the threads I feel reassured there is no problem with the design and charging of the 12 volt battery.

Yes there were reports of bad batteries and a report of a bluetooth console lockup.

It just doesn't work like we thought it did which is better as they made the design have less probability of damaging the 12 volt battery.

BobGPSr
04-25-2012, 08:36 AM
"indefinite trickle charging" that's a wide open statement. But a smart charger still should have a cut off voltage.
It is a simple matter to have the trickle charger set at less than the 13.8 volt maximum battery voltage, say set it to 13.5 volts, and protect against reverse current flow with a diode. No way to overcharge with this. No need for "smarts", just regulation.

WopOnTour
04-25-2012, 09:38 AM
What you are proposing is not only unnecessary but will overcharge the battery.
The potential issue on a showrooms floor is typically salesmen using "service mode" for demonstrating the Volt's instrumentation, audio system and interior features.
You're trying to solve a problem that doesn't exist.
WOT

silverton38
04-25-2012, 04:41 PM
I did a little experimenting and I was able to confirm that the 12 volt battery is not being charged while plugged in. After about a week of non-use. it turned off non critical functions such as OnStar. The battery voltage was low and a simple start/use of the car charged the battery. The battery is small and there are some drain devices such as OnStar.

marlow
04-25-2012, 06:52 PM
I did a little experimenting and I was able to confirm that the 12 volt battery is not being charged while plugged in. After about a week of non-use. it turned off non critical functions such as OnStar. The battery voltage was low and a simple start/use of the car charged the battery. The battery is small and there are some drain devices such as OnStar.

Im not sure what you mean buy the battery is small and the voltage being low. Sense the 12V battery in the Volt is not required to power the engine starter, I was actualy suprised that it was as large as it is. I would concider a 12 V lead acid batery as being low when ever its voltage is below 12.6 volts (without a significent load).

I did not know how long it took the battery protection to cut off un necessary drain from the battery, including that the Onstar functions will cease working after about a week of the Volt setting without use.

WopOnTour
04-25-2012, 08:38 PM
I did a little experimenting and I was able to confirm that the 12 volt battery is not being charged while plugged in.Again, it DOES charge the 12V battey while plugged in, assuming the Volt's Li-Ion battery isnt alrady fully charged that is.
If the Li-Ion battery is getting charged, then so is the 12V.
Once active charging of the Li-Ion battery stops though, so too does 12V charging.
So yes, techncially you CAN be plugged in and not getting a 12V charge but that is certainly not always the case.

After only a week of standing the 12V battery SOC would NOT be significantly "low" by almost any techncal definition but would of course be still recharged to a higher state, immediately after turning the car "ON".
WOT

BobGPSr
04-25-2012, 11:33 PM
What you are proposing is not only unnecessary but will overcharge the battery.

Wrong -- get your facts in order sir. When the trickle charger is set to a voltage less than the battery's normal maximum charge voltage, eventually all current flow into the battery is stopped and the battery cannot be overcharged.

scottf200
04-26-2012, 12:14 AM
Im not sure what you mean buy the battery is small and the voltage being low. Sense the 12V battery in the Volt is not required to power the engine starter, I was actualy suprised that it was as large as it is.<snip>Another aspect of where they made this car "normal". It can be used to jump start other cars (use post in the rear hatch). Heck it would seem like the APM (DC-DC converter) would provide a good load compared to a normal car with a alternator as your jumper. I'm pretty sure there was a thread on the MyNissanLEAF that stated you cannot jump other cars from your LEAF.

Related older thread: Auxillary-Battery
http://gm-volt.com/forum/showthread.php?5409-Auxillary-Battery

WopOnTour
04-26-2012, 02:59 AM
Wrong -- get your facts in order sir. When the trickle charger is set to a voltage less than the battery's normal maximum charge voltage, eventually all current flow into the battery is stopped and the battery cannot be overcharged.Ummm you do know the 12V battery is an Absorbant Glass Mat design don't you? Do you have expertise in AGM charging I take it? FWIW, AGM batteries require a specifc tapering charging schedule that is able to switch from current regulation to voltage regulation as it approaches 100% SOC in order to prevent overcharging (which AGM are quite prone to if placed in a standard lead-acid (purely voltage regulation) charge scheme.
The Midtronics battery charger used by GM Engineering and GM dealerships has a special "AGM" setting to facilitate this but...

Tell you what. It's your car.
Trickle charge it however you please,
but I'm here to tell you (well, mostly others) that it is 100% totally unecessary to do so.
Enjoy your Volt
WOT

BobGPSr
04-26-2012, 07:05 PM
Ummm you do know the 12V battery is an Absorbant Glass Mat design don't you?
Yes and it is my understanding that this Absorbed Glass Matt is just a variant of the Valve Regulated Lead Acid battery (a wet cell). GEL cells on the other hand require use of a special type of charger.

Here is a chart that shows AGM trickle charging in the bottom row, Optional Float Stage V2. Requires 2.25 volts/cell (13.5 volts total as I previously stated).

http://www.mkbattery.com/images/AGMBatteryCharging.pdf

I am not talking about doing a full charge on the 12 volt battery -- I'll let the Volt do that. The issue is long term maintenance of the 12 volt battery SOC after the propulsion battery is charged but the Volt is not used for an extended period.

cnicholson
04-26-2012, 07:56 PM
As far as your 12V battery not ever being run down while the Volt is "On" that of course depends on how long it will take for the Li-Ion battery to reach a critically low state of charge. (basically the equivalent of running out of gas idling on a conventional car) It won't start the engine in this event. Instead the system "load sheds" (to protect the Li-Ion battery from going too deep) and DC-DC conversion ceases andsince the power mode is still "ON" everything is being powered by the 12V battery eventually it will be dead as a door nail.

Is that true about the ICE not firing up when "On" and the main battery has been drained from charging the 12V? I thought in the thread about using the Volt as an emergency power source/generator it was reported that the ICE will kick on periodically to give the main battery a bit of a charge and then shut off as this new charge gets depleted by further charging the 12V. In the example, the 12V power power a load from a connected inverter.

Back to the main discussion. Although an edge case for sure, since the car can "know" that you are on the path to having a disabled vehicle (by watching the voltage on the 12V), wouldn't it be preferable in all cases (even when car if "off" and NOT plugged in) to periodically fire up the 12V charging function (once every 48 hours?) to avoid this bad scenario? Perhaps have the additional rule to not go below 33% SOC (or whatever) in so doing...

DonC
04-26-2012, 08:50 PM
Is that true about the ICE not firing up when "On" and the main battery has been drained from charging the 12V? I thought in the thread about using the Volt as an emergency power source/generator it was reported that the ICE will kick on periodically to give the main battery a bit of a charge and then shut off as this new charge gets depleted by further charging the 12V.In the other thread the Volt wasn't plugged in. Here it is plugged in. That's all.

cnicholson
04-26-2012, 08:55 PM
In the other thread the Volt wasn't plugged in. Here it is plugged in. That's all.

But if it is "on" and plugged in, the main battery would get depleted and charging would resume from the grid, wouldn't it? I thought Wop's case was the car unplugged but "on" (same as the emergency power case).

WopOnTour
04-27-2012, 12:18 AM
In the other thread the Volt wasn't plugged in. Here it is plugged in. That's all.
Is that true about the ICE not firing up when "On" and the main battery has been drained from charging the 12V? I thought in the thread about using the Volt as an emergency power source/generator it was reported that the ICE will kick on periodically to give the main battery a bit of a charge and then shut off as this new charge gets depleted by further charging the 12V. In the example, the 12V power power a load from a connected inverter.In this case you are both right.
Don, in that if you plug the Volt in while it is "ON" it will never meet the power mode requirements to commence charging. But as long as the DC-DC converter is able to get power from the Li-Ion battery the 12V battery will continue to be maintained (charged).

Mr. Nicholson is correct my wording was all messed in that post in which he has quoted me. (a case where I knew what I was trying to say, but while editing it got lost in translation)

YES, as we have said all along (going back to our emergency inverter discussions) if the Volt is left ON, once the SOC of the Li-Ion battery gets down to ~17-18% SOC the ICE will run, charge, and prop the SOC back up to ~20-21% where it will shut off. It will continue this cycle until it runs out of fuel (what I was trying to convey in that other post). Once out of fuel the SOC will continue to fall and at ~16% the sytem will go into load shedding, shutting off high-voltage sourced items like the coolant heater and A/C compressor and when it hits 15% it pulls the plug ont he DC-DC converter (saving the remaining charge on the HV battery) and the 12V battery would then be on it's own to drain to stone-cold dead. Of course,this scenario could also occur if the ICE could not start for some other reason. But in the case of the emergency generator, the gerry can is your friend of course.;)

Then back to Don's point. IF prior to this event you had plugged in your Volt while it was still ON (and didnt notice it didnt give you any "green" indication on the LED or horn chirp). When you walked up to this car a day you would have a dead 12V battery and out of gas. (and hopefully no dead cats int he garage!)

Merely unplugging-plugging in the J1772 connector (aka "cycling") in this case would do nothing as with a stone cold dead 12V the proximity and pilot circuits wont work. Boosting alone wont be much help as at only 15% SOC it's not letting the car go anywhere. However all one would really need to do in this scenario is first boost or put a charger on the 12V THEN "cycle" the J1772 plug, reinitiating the charge cycle. (and once it starts charging you can techncially stop boosting/charging the !@v source as it would get a charge from the on-board charging module)

Anyways, this is what I have found...
WOT

PS> Mr. Nicholson please go back and re-read that original post. I didt bother rewriting it, just "edited" it so it was correct and made sense. Feel free to let me know if it still has issues. ty

DonC
04-27-2012, 02:19 AM
I was thinking you were saying something else. Two separate states:

1. Volt is ON when you plug it in. My interpretation is that this is no different than not plugging in. The HV battery will charge the 12V battery and the engine will come on when the SOC falls to the depletion point. Similar to an ICE being ON.

2. Volt is OFF when you plug it in. After the EVSE is detected you turn the Volt ON. If charging then the 12V battery gets charged from the grid. If not charging, either outside the charging window or charging is complete, the HV pack will not maintain the 12V battery and the engine will not come on. You end up with a fully charged HV pack and a dead 12V battery. Similar to an ICE being OFF but set to Accessory position.

vdiv
04-27-2012, 10:05 AM
I think we beat this topic to death. Regardless of how many parallels are drawn to "normal" cars, the Volt is different in one very important regard, it is a plug-in vehicle. And while plugged in, with a fully charged 380V battery, and in a off/standby state there is no legitimate reason why it cannot keep the 12V battery charged. Move this to the GM Suggestions box and move on. Thanks.

cnicholson
04-27-2012, 10:39 AM
2. Volt is OFF when you plug it in. After the EVSE is detected you turn the Volt ON.....HV pack will not maintain the 12V battery and the engine will not come on. You end up with a fully charged HV pack and a dead 12V battery. Similar to an ICE being OFF but set to Accessory position.

This is confusing. Are you correct here? I thought the rule was: [ (Car is "on") or (Car is charging) ] = 12V gets charged.

My final dead horse question is: If you are plugged in, post charge completion and with car "off," will the car ever restart charging due to HV pack running low (would take weeks or months I suppose). I think the answer is NO. But, if turn "ON" while plugged in (either before or after charge completion) I had assumed that the car WOULD go back into charge mode to top off when HV runs low (consider the remote start case-- also perhaps a distinct mode). If true, then it seems like a safe indefinite storage mode is: plugged in and "on" (will continuously maintain the HV and 12V).

DonC
04-27-2012, 11:34 AM
I'm not sure that the rule is "ON" and plugged in is the same as "ON" and not plugged in. The discussions about having the car "ON" have always been in scenarios where it wasn't plugged in (power outages etc.). I don't know but my guess is that "ON" and plugged in and not charging is a separate state. For example, in this state you can't move the Volt out of Park.

With respect to your second question, my guess, which is more based on the Leaf than the Volt, is that it would depend on whether the timer was set. With the Leaf, once the charge is complete it just sort of goes dead. No lights and you have to unplug and replug it to initiate a charge. When the Volt finishes charging the green light flashes. My guess is that if there is another timer event and the SOC was low then it would charge. (This would be easy to test. Just set a short charging window and the long one five minutes later. See what happens.) Note that once a charge is complete there are reasons why you wouldn't want to "top off" in the absence of a charging event. If the temperature was dropping then you'd be reinitiating charging with some regularity. To avoid this I think you need some event to restart the monitoring process -- like unplugging and plugging (Leaf or Volt) or the start of a new charging window (Volt).

Note that it's not recommended that you plug it in when storing the car for extended periods. You want the SOC to be low, so the recommendation is to disconnect the 12V battery and have the SOC of the HV pack to be less than 50%. If you had a way of setting charging to a low SOC like 30%, then plugging in might work, but this would be problematic for the 12V since the charging wouldn't be long enough to maintain it. And when the 12V went south the car wouldn't initiate charging.