Amp-hour (Ah)

Amp-hours tell you how much charge is in the tank. Milliamp-hours (mAh) are the same thing in smaller units: 2,400 mAh is 2.4 Ah.

Wiring cells side by side adds amp-hours. Battery University’s laptop example takes a 2,400 mAh pack to 4,800 mAh by doubling up the cells, while the voltage stays the same.

The catch is that amp-hours only compare fairly between packs of the same voltage. For packs of different voltage, use watt-hours instead.