Amp-Hour

An amp-hour (Ah) is the charge delivered by a current of one amp flowing for one hour. It is the usual capacity rating for 12 volt car, RV, boat and solar batteries.

Charging time in hours is amp-hours needed divided by charger amps, after allowing for losses. A 100 Ah lead-acid battery charged from empty at 90% efficiency needs 111.1 Ah, which takes about 11 hours 7 minutes on a 10 amp charger. The battery charging time calculator uses this formula.

Multiply amp-hours by volts to get watt-hours: 100 Ah at 12 volts is 1,200 Wh. That conversion lets you compare a battery with a solar panel in the solar charging time calculator.