An amp hour (Ah) is a unit of electric charge that measures the amount of energy charge in a battery that enables 1 ampere of current to flow for one hour. It is a measure of how long a battery can provide one amp of power per hour. One ampere of current represents 1 coulomb of electrical charge moving past a specific point in one second. Mathematically, Ah is represented as the following: Amp hour (Ah) = Current (I) x Discharge time (T). For instance, a battery with a 10 Ah rating will last twice as long as a battery with a 5 Ah rating when used under similar conditions, but it does not mean that it will actually last 10 full hours. The commonly seen milliampere-hour (mAh) is one-thousandth of an ampere-hour (3.6 coulombs). Amp hours are used to describe the capacity of an energy storage device, such as a rechargeable battery or deep-cycle battery.