paperlined.org
sports > backpacking > CPAP
document updated 7 years ago, on Apr 18, 2015

battery types

A normal car battery (lead-acid) isn't designed to be discharged very much. It's designed for very-short-term surge applications, not for running things overnight.

A deep-cycle battery (AKA marine battery) is designed to handle a load for hours at a time.

cutoff percentage

If you don't want to deep-cycle a normal lead-acid battery, then you should cutoff the battery at 80-90% charge. That website says this equates to 12.4 volts.