Milliamperehours

Milliampere-hours (mAh) is a unit of electric charge commonly used to describe the capacity of batteries in portable devices. It indicates how much charge a battery can deliver before its voltage falls below a usable level. The term milliampere-hour equals one thousandth of an ampere-hour; since one ampere-hour equals 3,600 coulombs, 1 mAh equals 3.6 coulombs.

Capacity and runtime: A battery rated at X mAh can deliver X milliamperes for one hour, or a larger current for proportionally shorter times, in principle. For example, a 3000 mAh cell discharged at 1000 mA would last about 3 hours, neglecting inefficiencies. In practice, runtime depends on discharge rate, temperature, chemistry, and the device’s actual power use.

Energy relation: mAh measures charge; energy is charge times voltage. To compare energy, multiply the capacity in Ah by the nominal voltage to obtain watt-hours (Wh). For a 3000 mAh cell at 3.7 V, the energy is about 3 Ah × 3.7 V ≈ 11.1 Wh (11,100 mWh).

Discharge rate effects: Capacity is specified under standard test conditions. At higher discharge rates, usable capacity may decrease (Peukert effect), and voltage can sag, reducing actual runtime.

Usage and examples: Common battery types rated in mAh include Li-ion, Li-polymer, and NiMH. Smartphone batteries typically range from about 3000 to 5000 mAh; AA alkaline cells range roughly 1700–3000 mAh at low drain; 18650 Li-ion cells often 1200–3500 mAh.