Watt hour

A watt hour (Wh) is a unit of energy equal to using one watt of power for one hour, or 3,600 joules. Battery capacity is often given in watt hours because it tells you how long a pack can supply a given power. A 100 Wh battery can in principle run a 100 W load for one hour or a 50 W load for two hours.

Example: A typical laptop battery holds around 50 watt hours, enough to run a 10 watt laptop for about five hours.