Runtime
7.65hours
Estimated steady-load runtime after efficiency and reserve.
Portable Power Station Runtime Calculator
Estimate how many hours a portable power station can run a device after inverter losses and battery reserve.
Use this when you know the battery capacity in watt-hours and the device load in watts. The result is a steady-load estimate; real runtime can change with temperature, battery age, device cycling, inverter behavior, and manufacturer limits.
Runtime inputs
Wh
Use the rated watt-hours from the power station label or manual.
W
Use the device running watts, not surge watts.
%
85% is a reasonable default for AC inverter use.
%
Energy kept unused to avoid planning around a fully drained battery.
W
Optional. Leave blank if you only want the runtime estimate.
Results
Runtime
0.32days
Usable energy
765Wh
Efficiency loss
150Wh
Reserve kept
85Wh
Calculation breakdown
| Item | Value | Notes |
|---|---|---|
| Rated capacity | 1,000 Wh | Starting battery energy before losses. |
| After inverter efficiency | 850 Wh | 85% efficiency applied. |
| Usable energy | 765 Wh | 10% reserve kept unused. |
| Runtime | 7.65 hours | 765 Wh / 100 W load. |
Formula
runtimeHours = capacityWh x (efficiencyPercent / 100) x (1 - reservePercent / 100) / loadWattsIf the load is greater than the optional continuous output rating, the calculator displays a warning because runtime is not the only limit. The power station must also be able to supply the load.
- capacityWh
- The rated battery capacity in watt-hours.
- efficiencyPercent
- The percentage of stored energy estimated to reach the device after inverter losses.
- reservePercent
- The percentage of post-efficiency energy kept unused for planning margin.
- loadWatts
- The connected device running load in watts.
Example
This example assumes a steady AC load. A cycling refrigerator, heater, pump, or power tool can vary from the estimate.
- Battery capacity is 1,000 Wh.
- The connected device uses 100 W.
- Inverter efficiency is 85%, leaving 850 Wh after efficiency loss.
- A 10% reserve keeps 85 Wh unused, leaving 765 Wh usable.
- 765 Wh divided by 100 W gives about 7.65 hours of runtime.
How to use this calculator
- Enter the power station battery capacity in watt-hours.
- Enter the device running load in watts.
- Keep the default 85% efficiency unless you have a better estimate for the device and output type.
- Enter a continuous output rating if you want an overload warning.
Input guide
- Battery capacity: stored energy, usually printed as Wh on the power station specification.
- Load watts: the running power draw of the device you plan to plug in.
- Inverter efficiency: estimated conversion loss when using AC output.
- Battery reserve: energy intentionally left unused for planning margin.
- Continuous output rating: optional watt rating used to warn when the device load may be too high.
Common mistakes
- Assuming rated watt-hours are fully usable at the outlet.
- Ignoring the continuous output limit when running larger loads.
- Using surge watts instead of normal running watts for runtime.
- Expecting a cycling or temperature-sensitive device to match a steady-load estimate exactly.
Limitations
The formula assumes a steady load and a single efficiency value. It does not model manufacturer reserve settings, battery age, cold weather performance, DC output behavior, startup surge, pass-through charging limits, or changing loads over time.
FAQ
Why is usable energy lower than the label capacity?
Inverter losses and battery reserve reduce the watt-hours available to the connected device.
What if my device load is higher than the output rating?
The power station may shut off, overload, or fail to start the device. Check the continuous and surge ratings before use.
Should I use rated capacity or usable capacity?
Use rated capacity if that is the only value available. The calculator then estimates usable energy after inverter efficiency and reserve.
Can I use this for devices with changing loads?
Yes, but use an average load estimate. Devices with compressors, heaters, or variable speed motors may run longer or shorter than a steady-load estimate.
Related calculators
Use these tools to compare runtime with refrigerator, CPAP, and solar charging estimates.
- Refrigerator Backup Time CalculatorEstimate refrigerator or freezer backup time using battery capacity, duty cycle, and inverter efficiency.
- CPAP Battery Backup CalculatorEstimate CPAP backup runtime and nights from battery capacity, humidifier use, reserve, and efficiency.
- Solar Panel Charging Time CalculatorEstimate solar charging time from battery size, charge target, panel watts, sun hours, and system efficiency.
Methodology and disclaimer
Runtime is an estimate based on rated watt-hours and steady load. Actual results vary with device behavior, temperature, battery age, inverter limits, and manufacturer settings.
The calculator multiplies rated capacity by inverter efficiency, subtracts the chosen reserve, then divides usable watt-hours by the connected load in watts.