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Portable power station runtime calculator
Estimate how long a portable power station will run a fridge, CPAP, router, lights or any mix of devices, including inverter losses, idle draw and output limits.
Results
| Estimated runtime | 7 h 58 min |
|---|---|
| Combined running load (AC side) | 93 W |
| Draw from the battery incl. losses | 116 W |
| Usable energy | 922 Wh |
| Continuous output used | 5 % |
| Estimated start-up peak | 1,233 W |
- Real runtime is usually within about ±15% of this estimate. Cold batteries (below about 40 °F / 5 °C) and old batteries run shorter.
About this calculator
Spec sheets tell you the battery size in watt-hours. They don't tell you how long that battery will keep your devices running. The answer depends on three things the headline number leaves out: the share of the battery you can actually use, the energy the AC inverter loses as heat, and the small but constant power the inverter uses just by being switched on.
This calculator accounts for all three. List the devices you plan to run at the same time and it estimates the runtime, then checks two limits people often miss: whether the combined load fits under the continuous output rating, and whether the start-up surge of a fridge or pump fits under the surge rating.
How to use it
- Enter the rated capacity in Wh from your power station's spec sheet. If only amp-hours are listed, convert them with the Ah to Wh converter.
- Leave usable share, inverter efficiency and idle draw at the defaults unless your manual or your own testing says otherwise.
- Add each device you will run at the same time. For appliances that cycle on and off, such as fridges and freezers, enter the average draw, not the running watts.
- Read the runtime and check the warnings. If the load is close to the output limit, the station may also run its fans and lose a little more energy.
The formula
Usable energy = rated Wh × usable %.
Battery draw = (sum of device watts ÷ inverter efficiency) + inverter idle watts.
Runtime (hours) = usable energy ÷ battery draw.
Start-up peak = sum of running watts + the single largest (starting − running) difference. Usually only one motor starts at a time, so the largest surge is the one that matters.
Worked example (default values)
Inputs
| Rated battery capacity | 1024 Wh |
|---|---|
| Usable share of rated capacity | 90 % |
| Inverter efficiency (AC outlets) | 88 % |
| Inverter idle draw | 10 W |
| Continuous output rating | 1800 W |
| Surge (peak) output rating | 3600 W |
| Devices running at the same time | Refrigerator (full size, average draw): 60 W; Wi-Fi router + modem: 15 W; LED light bulb: 9 W × 2 |
Results
| Estimated runtime | 7 h 58 min |
|---|---|
| Combined running load (AC side) | 93 W |
| Draw from the battery incl. losses | 116 W |
| Usable energy | 922 Wh |
| Continuous output used | 5 % |
| Estimated start-up peak | 1,233 W |
Tips and common mistakes
Fridges are the classic trap. A full-size fridge might pull 120-180 W while its compressor runs, but the compressor is only on roughly a third to half of the time. Its average draw is often 40-80 W. Enter the average, or measure 24 hours of use with a plug-in energy meter and divide the Wh by 24. If you enter the running watts instead, the calculator will underestimate runtime by half or more.
Use DC ports when you can. Running a router, CPAP or fan from the 12 V or USB-C ports skips the inverter entirely. That avoids both the conversion loss and the idle draw, which can add 20-40% more runtime for small loads.
Frequently asked questions
How long will a 1000 Wh power station run a refrigerator?
A typical modern full-size fridge averages about 40-80 W over a day. A 1000 Wh station delivers roughly 800 Wh after losses, so expect about 10-18 hours. Older fridges, hot kitchens and frequent door opening shorten that.
Why does my station die sooner than capacity ÷ watts?
That simple division ignores inverter losses (often 10-15%), idle draw (5-20 W) and the reserve the battery management system keeps. A 100 W load on a 1000 Wh station usually lasts closer to 7-8 hours than 10.
Does a bigger continuous output rating give more runtime?
No. Output rating (W) decides what you can power. Capacity (Wh) decides for how long. A bigger inverter can even have a slightly higher idle draw.
Can I run devices while the station is charging?
Most stations support pass-through charging. When they're plugged into the wall, devices run from the grid and the battery doesn't drain. Check your model's manual for UPS or bypass behavior.
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Estimates for planning only, based on the assumptions shown. Real-world performance varies with equipment, temperature and installation. Updated October 19, 2026. See our methodology.