Sometimes, I'll know that I have quite a few miles to go before charging, and my battery is nearly empty. I've been toying with the idea of going into Mountain Mode for a few miles and letting it charge up the battery a little bit so that I can drive on electricity for a little longer. My idea is that you'll spend a couple miles with the ICE on and generating electricity, and then you'll have some pure electric miles in the battery after switching back to Normal mode. Hopefully, the miles spent in MM, plus the electric miles in the battery at the end of it would equate to more miles than the same amount of gas would have sent you in CS mode. Note, I am just driving on normal streets and highways, not mountainous roads which would actually need Mountain Mode.
I'm wondering if the car charges the battery more efficiently in Mountain Mode since it is always running at a constant, higher rate instead of fluctuating as you drive like in CS mode. My understanding of CS and Hold modes is that the ICE kicks in at appropriate time and throttle so that the battery will just stay at the given SOC, with the car still being powered by the battery (except for extenuating circumstances where the ICE connects directly to the wheels).
I have not done this yet, it's merely an idea, so I was wondering if anyone else had any thoughts/experience/data about it.