Energy in a battery is measured in Watt-hours; what does this unit represent?

• A. The energy content
• B. The instantaneous power
• C. The current draw
• D. The voltage level

Answer: (A)

Watt-hours quantify the total energy stored in a battery—the amount of energy it can deliver over time. Power (watts) is the rate at which energy is used, and multiplying that rate by the time over which it’s delivered gives energy in watt-hours. So watt-hours describe the battery’s energy content.

The other terms measure different things: instantaneous power is the current rate of energy transfer (watts) at a moment, current draw is the flow of electric charge (amps), and voltage is the electrical potential difference (volts) at a given moment. If you know the energy content (in watt-hours) and the device’s power draw, you can estimate how long the battery will run. For example, a 7.4 Wh battery could power a 7.4 W device for about one hour.