A current flow for one hour measured in amperes (amps). Abbreviated "Ah" and commonly called "amp-hour," it is widely used to rate how long it takes for a battery to discharge. For smaller batteries, a milliampere-hour (mAh) rating is used. For example, a 500 mAh battery means it will release 500 milliamps of current at a specific voltage for one hour before it is discharged. See ampere
Amp-Hours and Watt-Hours
Batteries can be rated in amp-hours (Ah) or watt-hours (Wh) as shown in these examples for a digital camera. The bottom battery is equivalent to 3.3 Wh, while the top battery is equivalent to 667 mAh.