When Uberwasser, Iridium, and I took our cars up to Phoenix to go junk yard hopping together, Iridium's car had the voltage regulator fail stranding him at one of the yards we stopped at. It was running fine, he shut it down, then he had no life signs. We took the battery out and brought it to Autozone to be charged and tested. It was fine, so he put it back in his car, started it up, and we headed back for Tucson.
His regulator must have failed on the trip up, and the power draw from his radio, blower motor, and other electric gadgets drained the battery on the way up. Once he shut it off, we were stuck. After charging, it was good to go until he shut it off again.
We left before sundown and traveled in convoy formation so he wouldn't be without lights if he needed them.