[brucepick]

WeatherSpotter,

Do you want to drive with alternator disabled? Or are you simply trying to have a reasonable EOC distance with headlights and some accessories running?

I think a deep cycle in the standard location will be fine for nice EOC opportunities if alternator is in use when engine is running. If you get a really long mountain downgrade coast (several miles), I expect you can put it in gear, keep coasting, and that will run your alternator just fine.

OTOH, if you want to drive without alternator on a regular basis, you'll likely need more amp hours capacity (aka reserve capacity) than what you can fit in the regular front battery tray. Thus my approx 140AH of battery capacity that I have in my trunk. That's 5.6 hours of reserve, as the spec is service time at 25 amps draw (140AH/25A = 5.6 hours).

But my commute is about 1.25 hours each way, and I want to be able to do that PLUS some lunch time errands if I care to. So I want to be ready for over 3.5 hours drive time WITH headlights on, or 6+ hours without headlights. And I bought more capacity than what I need because you don't want to regularly deeply or fully discharge lead acid batteries.