I wonder if there's anyone who could tell me what is the minimum voltage to which a car battery can be discharged without any permanent damage, and still be capable of starting the engine?
The reason I'm asking is that I sometimes run a small portable fridge in my car which is fine while the engine is running but would obviously soon flatten the battery if it were not (it takes about 4A). This doesn't arise at the moment as I plug the fridge into the cigarette light socket on my present car, which is switched off with the ignition. However I'm thinking of changing the car to one which apparently has a 12V power socket in the boot which would obviously be much more convenient for the fridge, *but* it's permanently live.
I have a small device which is supposed to protect the battery against accidental discharge by switching off when the voltage drops below a "safe" level. I've checked it with a DVM though and it allows the voltage to drop to
10.6V before switching off. This seem to me much too low for safety - hence my question.