Watt-hour
A watt-hour (Wh) is a measure of energy: the power in watts multiplied by the hours it runs. Watt-hours are a common way to state how much energy a battery can store, so they help you judge how long a battery might last with a given item.
Where you'll see it
You'll find watt-hours on battery and portable power station labels, and on product pages for leisure batteries. Some batteries are rated in amp-hours (Ah) instead. Amp-hours are a different unit, so convert only if the label or maker gives the voltage you need. Real results vary with the item, the temperature and the battery's age.
What to check
- Whether the capacity is stated in watt-hours (Wh) or amp-hours (Ah), and the unit printed on the label.
- The power output and sockets the maker lists, so you know what the battery can supply.
- The run-time estimate the maker gives, and what it assumes about the item you would run.
- The maker's guidance on charging, storage and use outdoors.
Related terms
- Watt: the power that, multiplied by hours, gives watt-hours.
- Portable power station: a battery unit whose capacity is often given in watt-hours.
- Leisure battery: a battery for camping use, with its capacity on the label.
Read more: Camping without hook-up (UK) and the off-grid power needs calculator.