Energy in a battery is measured in which unit?

• A. Amp-hours (Ah)
• B. Watt-hours (Wh)
• C. Volts (V)
• D. Watts (W)

Answer: (B)

Energy stored in a battery is the total amount of energy it can deliver, which depends on both the charge it holds and the voltage at which that charge is delivered. Watt-hours express this neatly because they combine voltage with the charge capacity: energy equals voltage times amp-hours. Amp-hours tell you how much charge is available, but not how much energy, unless you know the voltage. Volts measure potential difference, not energy, and watts measure the rate of energy transfer (power), not the total energy. So watt-hours is the unit that quantifies the total energy stored in a battery.