[neallewis]

Originally Posted by mark christopher

Car batteries are not designed for deep discharge and if you drop it below a certain voltage, not even flat, your car will probably not charge, if it's modern as dave says it will probably be ignition fed, and probably even shut down via body module.

Leisure battery or a generator for outdoors

I've used my old bosch 110 (85Ah) car battery for for the last 5 years during summer season. It gets charged the night before a meeting, and allows me to charge enough packs for running two cars at 6-8A. It's also lasted me over weekend races without recharge, and allowed a club member to also charge on occasion. Car batteries are fine for charging if you don't run them flat, or expect them to start your car. I race weekly thought the summer, so it gets plenty of cycles. Every year I've expected it to fail, but it carries on fine. When it eventually fails, i'll buy a new one for my car, and do the same with the old one.