Ampèrehour

Ampere-hour (Ah) is a unit of electric charge that represents the amount of charge transferred by a constant current of one ampere flowing for one hour. It is commonly used to describe the capacity of rechargeable batteries and other energy storage devices.

Because one ampere equals one coulomb per second, 1 Ah is equal to 3600 coulombs. The ampere-hour is convenient for measuring how much charge a battery can deliver, but it is not a unit of energy. The energy stored in a battery is the product of its voltage and its charge, so energy in watt-hours equals voltage in volts times capacity in ampere-hours (Wh = V × Ah). For example, a 12 V battery rated at 100 Ah stores about 1200 Wh of energy.

In practice, the usable Ah can vary with operating conditions. Capacity is affected by discharge rate, temperature, battery age, and the end-of-discharge voltage used during operation. Therefore, manufacturers often specify Ah at a particular discharge rate (for example, at 0.5C or 1C) and a nominal voltage.

Ah is widely used for batteries in automotive, consumer electronics, and renewable energy systems. A smaller unit, milliampere-hour (mAh), is common for small devices.

The ampere-hour is a non-SI unit that is accepted for use with SI, and it is named after André-Marie Ampère.