I found this useful deep-cycle battery FAQ that included a rough voltage level chart which helps you determine how full your deep-cycle battery is: State of Charge12 Volt batteryVolts per Cell100%12.72.1290%12.52.0880%12.422.0770%12.322.0560%12.202.0350%12.062.0140%11.91.9830%11.751.9620%11.581.9310%**11.31**1.89010.5**1.75** While I haven’t blogged about it, I have a small solar panel setup on my patio which provides enough power to run a few lights in my living room each night for a few hours. This information lets me know how charged the battery system is. Right now my battery is at 12.75 ...