Energy

Energy is the work done, or in the case of batteries the ability or capacity to do work. It is power × time. Electrical energy is expressed as kilowatt-hours (kWh), which is the amount of power in kW transferred (or used) for 1 hour. It is also expressed as megawatt-hours (MWh); a MWh is equal to 1,000 kWh.

The average household electricity use in the USA is about 11,000 kWh per year.