Watts are not watt-hours
Power is the rate of energy transfer. Energy accumulates over time.
In 30 seconds
- For steady DC, P = V × I.
- Energy in Wh equals constant power in W multiplied by hours.
- Real batteries and converters have losses and operating limits.
Make it concrete
An ideal 20 W load for 3 hours uses 60 Wh. This arithmetic alone cannot size a real battery for a ship.
- 01Power W
- 02Time h
- 03Energy Wh
Check your understanding
Does a 20 W device running twice as long use twice the energy if its power stays constant?
- For steady DC, P = V × I.
- Energy in Wh equals constant power in W multiplied by hours.
- Real batteries and converters have losses and operating limits.
Go to the source
Sources reviewed: 13.09.2026