No- not the Volt, but it is the Volt’s fault! And this same thing might happen in a Volt. So I’ve mentioned a couple times that the 2008 Toyota Highlander Hybrid was going to my daughter. After not operating it in ?? weeks (that’s why it’s the Volt’s fault), I wanted to get it ready to go tomorrow to take it to her. Nothing- dead 12v means no start, no locks, no windows, nada. This vehicle also has keyless entry and I have them both in my hand (big mistake) because I am getting everything ready to go. I pop open one of the (never used) mechanical keys and unlock the door. I proceed to unlock all doors from inside and set the keys on the seat. I get the charger out and hook up everything. HOLY CRAP, horn starts blaring, I panic and disconnect charger. I then reconnect charger at trickle amperage. No horn. BUT….the process LOCKS ALL THE DOORS…with BOTH my keys inside. Ordinarily, Toyota won’t let you lock your keys inside, but obviously that process goes screwy with dead 12v battery.

I call AAA to get me back into car, and give me a jump start. Here is where the story needs some answers for me, for anyone who has experienced dead 12v hybrid. It is weird, after a lifetime of jumping ordinary cars to experience the process in a hybrid. The car starts, but without engine. As would normally be the case, ICE starts shortly thereafter. HOWEVER, (and this is what I would like to know for Volt, or any other hybrid I will own in future), YOU CAN’T JUST LEAVE THE CAR RUNNING TO RESTORE THE 12V SYSTEM (or so it would seem). Ironically, while 12v was dead, high voltage battery was still fine- so ice shuts off….so HOW is my 12v going to get charged?? I drive it around the neighborhood. Everything is okay. Maybe a half mile, I rev the engine here and there to make sure ICE stays on. I even pull it in driveway, turn it off and turn it back on and go for another short spin, take it home and shut it off again.

[Just AFTER I put away the charger] I go to open tail gate- dead again. I get the charger back out. After few minutes on the charger, I am able to start up again. BUT I AM LEAVING IT ON THE CHARGER for a long time this time.

In the old days, if the battery wasn’t shot, driving around the car for a little bit should give you enough jolt from the alternator to get you ready to go start up again. With a hybrid, how are we supposed to know it is safe to turn ‘off’ the car, since ICE is not actually running to actually recharge battery. I had hoped that high voltage battery would do SOMETHING to ensure its smaller sibling wouldn’t crap out again. But that does not seem to be the case.

So my hybrid sits on the charger- until I see it go back to green on the battery charge indicator- and if it doesn’t, I go buy another 12v battery. What have others experienced with their Volts (or other electrics with regular engines that turn themselves off, even though a 12v battery is screaming for some juice)? While I have learned a couple things today (ie DON’T LEAVE KEYS IN TOYOTA HYBRIDS WITH DEAD BATTERIES; IT WILL LOCK YOU OUT EVEN THOUGH ALL DOORS WERE ALREADY UNLOCKED!!), I would like to know a little more about how to deal with this situation properly.

I'm not positive, but I believe the Toyota HSD hybrids use a DC-DC converter to charge the 12V battery, like the Volt does. Assuming that's correct, leaving the car on will charge the 12V battery even though the engine isn't running (by draining trivial amount of power from the Traction battery.) That is certainly the case with the Volt.

I would expect that like the Volt the HiHy would require very little power to start (compared to cranking an ICE, anyway) - and that your 12V battery is shot (leaving them discharged for long periods can do that.) Otherwise I'm not sure why you got the repeated failures.

In reading other threads (and saghost response), I see that if vehicle is 'on', high Voltage battery charges 12v. So given cabling, module capacity and other considerations, would it be better to let the vehicle just sit there in the driveway in an 'on' state or turn it off and do the job the old fashioned way with 10 amps on a battery charger?

[I will probably go get another battery and replace it. It is just over 4 years old and it is not worth the risk to leave my daughter stranded. But it would seem good to know the best way to deal with an accidentally discharged 12v battery in the future.]

My rule of thumb is if you experience even the slightest problem with a 12v lead acid starter battery it gets replaced. Yes you can play roulette with it by connecting a charger and making it look like it is good to go, but it isn't worth being stuck somewhere that isn't very convenient with a dead battery.

If you care about your daughter, get her a new battery.

VIN # B0985

Update: I got a new battery; boy have they gone up in price. The last time I remember getting batteries, they were approx $70- and for batteries with much more substance than the one I just bought (Advance Auto Parts) for $100. As mentioned previously, and in aggreement, AZ EV, it ain't worth getting stranded, especially since my daughter will be using this as a work vehicle.

But if this were, let's say, just over two years old, I'd not be so quick to pronounce it worthless and would still like to know- better/faster to charge with 10 amp (external) charger or just leave it 'on' and let its big brother battery do the job?

Honestly, I doubt it matters much. The only thing that could make a difference is the intelligence of the two charging systems for controlling the rate of charging and preventing overcharging. For the second half, I'd assume both will do a good job. The first part, I don't know if the vehicle system does anything to limit charging rates... The external charger is probably the safer bet, but I doubt either one would produce an issue.

First of all, with OnStar, locking the keys in the car would be a non-problem.

Second, with any (rechargeable) battery, replacing the battery just because it ran down would be like replacing a gas tank when you ran out of gas. Yes, you would replace a tank if it didn't hold gas, and you would replace a battery if it can't hold a charge.

There is the root cause. Is the lead-acid battery old and degraded? (they can be load tested). Is there some add-on electrical load, such as the alarm you added on? What is the expected stand time for your vehicle? Most should handle 2-3 weeks.

Finally, related to the Volt - be cautious about using a trickle charger. (I'm not sure why one wouldn't want to drive the Volt for an extended period, but some put it in storage over the winter). The AGM 12 V battery is susceptible to overcharge, so only use a charger made for AGM batteries. With the charging capacity of the Volt, should it ever run down the 12V battery (it turns off lights that might be left on; maybe you had the radio playing during a 3 hour tailgate party in the accessory / service mode without the HV battery active), just take it out for a nice pleasant ride and the 12V battery will be full within 30 minutes, I would imagine.

Well us desert dwellers figure that the OEM battery is doing good if we get 4 years out of it. After that, we play the revolving battery game with the FLAPS (that's Friendly Local Auto Parts Store) roughly every 2 years. It's not a good thing to have a "compromised" battery when the temps are well into triple digits. It's just not worth it.

VIN # B0985

I agree with AZ EV Driver, a 2008 car is due for a new battery, and messing with chargers, jumper cables, and being stuck is simply not worth it. With cars packed with electronics these days, messing with the electrical system could become disastrous.