What is an Amp Hour?

An Amp-Hour or ampere-hour (Ah) describes battery capacity - how long will it run before it is drained. Suppose you have a 100 Amp-hour battery, typically tested over a 20 hour period. 100 Amp-hours divided by 20 hours = 5 amps. That means that the manufacturer claims the battery can sustain a 5 amp load for 20 hours until the battery is completely dead.