What is the minimum allowable discharge voltage for maximum life of a standard 12-volt lead-acid battery?

Answer: C. 10.5 volts

Discharging a 12-volt lead-acid battery below about 10.5 volts shortens its life. Stop discharging at 10.5 V to get the most charge cycles.

Tip: Lead-acid: stop at 10.5 volts.