Explainer
Watts, watt-hours and amp-hours explained
The three numbers on every battery and how they relate.
Published
- Watts (W) are a rate of power; watt-hours (Wh) are an amount of energy.
- Watt-hours = volts × amp-hours.
- A 100 Ah battery at 12 V holds about 1,200 Wh; at 48 V it holds about 4,800 Wh.
Power vs energy
Watts measure how fast a device uses energy right now. Watt-hours measure how much energy is used or stored over time. A 100 W device running for 3 hours uses 300 Wh.
Why amp-hours mislead
Amp-hours (Ah) describe charge at a particular voltage. Two batteries both labeled 100 Ah can hold very different amounts of energy if one is 12 V and the other is 48 V. Convert to watt-hours before comparing.
Kilowatt-hours
1 kilowatt-hour (kWh) = 1,000 Wh. Utility bills, home batteries and electric vehicles usually use kWh.
Quick conversions
| Battery label | Approximate energy |
|---|---|
| 12 V 100 Ah | 1.2 kWh |
| 24 V 100 Ah | 2.4 kWh |
| 48 V 100 Ah | 4.8 kWh |
| 12.8 V 280 Ah | about 3.6 kWh |
FAQ
Where do I go next?
Try the power planner to put numbers to your own situation, or see the product picks on the deals page.
Terms used here
- Watt (W)
- Rate of power use or production.
- Watt-hour (Wh)
- Energy: one watt for one hour.
- Kilowatt-hour (kWh)
- 1,000 watt-hours.
- Amp-hour (Ah)
- Battery charge capacity at a given voltage.
This guide is informational and based on published specifications and general references, not hands-on testing. Check the manufacturer's current specs before you buy.