How this calculator works
Battery capacity is a quantity of energy, and a device's power draw is a rate. Divide energy by rate and you get time. Amp-hours need converting first: watt-hours = amp-hours × volts. We also allow for the part of the capacity you cannot use, because of inverter losses and, for lead-acid batteries, because they should not be drained below about half.
Worked example: a 1,000 Wh power station at 85% usable has 850 Wh to give. A 100 W load runs it for 8.5 hours. A 12 V, 100 Ah battery is 1,200 Wh, so at 85% and 100 W that is 10.2 hours.
Runtime in hours at 85% usable capacity
Rows are the load; columns are the battery size.
| Load | 300 Wh | 500 Wh | 1,000 Wh | 2,000 Wh | 3,000 Wh |
|---|---|---|---|---|---|
| 25 W | 10.2 h | 17.0 h | 34.0 h | 68.0 h | 102.0 h |
| 50 W | 5.1 h | 8.5 h | 17.0 h | 34.0 h | 51.0 h |
| 100 W | 2.5 h | 4.3 h | 8.5 h | 17.0 h | 25.5 h |
| 200 W | 1.3 h | 2.1 h | 4.3 h | 8.5 h | 12.8 h |
| 500 W | 0.5 h | 0.8 h | 1.7 h | 3.4 h | 5.1 h |
| 1000 W | 0.3 h | 0.4 h | 0.8 h | 1.7 h | 2.5 h |
| 1500 W | 0.2 h | 0.3 h | 0.6 h | 1.1 h | 1.7 h |
Tips before you buy
- Find the real load with a plug-in watt meter. It takes the guesswork out, and shows how a fridge or heater actually cycles.
- Heating and cooking appliances draw 1,000 W or more and empty a power station in under an hour. Do not plan on running them.
- Run devices in an eco or low mode where possible. Turn off lights and inverters you do not need.
- Inverters use some power even with nothing plugged in, so turn the AC output off when you are only charging USB devices.
- Cold weather can reduce capacity by 20% or more, so expect shorter runtime in winter.
Quick answers by size
Tools & materials for this project
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Frequently asked questions
How long will a 1,000 Wh power station run a refrigerator?
A typical full-size fridge averages 50 to 100 W over a day, so a 1,000 Wh station at 85% usable (850 Wh) lasts about 8 to 17 hours. Newer, efficient models last longer.
How do I convert amp-hours to watt-hours?
Multiply by the voltage. A 12 V 100 Ah battery holds 1,200 Wh. A 24 V 100 Ah battery holds 2,400 Wh.
How long will a 500 Wh power station run a laptop?
A laptop uses about 60 W, so 500 Wh at 85% usable runs it for roughly 7 hours, or two to four full charges of the laptop battery.
Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.