Ampèrehora

Ampèrehora, abbreviated as Ah, is a unit of electric charge widely used in electrical engineering and battery technology. It is defined as the amount of charge transferred by a constant current of one ampere flowing for one hour.

One ampèrehora equals 3600 coulombs, since a current of one ampere for one hour corresponds to 1 A × 3600 s = 3600 coulombs. The coulomb is the SI unit of electric charge, so the ampèrehora is a practical, non-SI unit that reflects charge or storage capacity rather than energy.

In practical terms, the Ah rating expresses how much charge a device or storage system can deliver. It does not specify energy by itself; to estimate energy, the voltage must be known. The energy stored is commonly expressed in watt-hours (Wh) and equals voltage (V) times charge in ampere-hours (Ah). For example, a 12 V battery rated at 100 Ah stores about 1200 Wh (1.2 kWh) of energy under ideal conditions.

Usability and performance depend on factors such as discharge rate, temperature, and aging, which can cause the actual usable capacity to differ from the rated Ah. The ampèrehora remains a convenient measure for comparing battery capacities and for calculating expected runtime when voltage is known. See also coulomb, watt-hour, and battery capacity.