“How long does it last?” has two meanings: runtime on one charge and the battery’s service life over years. This guide calculates both without confusing watts, watt-hours or inverter ratings.
Portable power station runtime formula
For an AC appliance, a realistic estimate separates the station’s usable battery energy from the battery-side power needed by the inverter.
A quick estimate that only uses capacity ÷ watts is optimistic because it ignores energy reserved by the battery-management system, inverter conversion loss and the inverter’s own power use.
Worked example: 1,000 Wh station and 100 W appliance
- Rated battery capacity: 1,000 Wh
- Usable capacity: 90%, giving 900 Wh
- AC inverter efficiency: 85%
- Power station idle draw: 5 W
- Battery-side draw: 100 ÷ 0.85 + 5 = 122.65 W
- Estimated runtime: 900 ÷ 122.65 = 7.34 hours
Real results can still change with temperature, battery age, the appliance’s duty cycle and whether its load varies over time.
Runtime table by battery size and load
The estimates below assume 90% usable capacity, 85% inverter efficiency and 5 W of station idle draw. They are planning figures, not product guarantees.
| Battery capacity | 20 W load | 60 W load | 100 W load | 500 W load |
|---|---|---|---|---|
| 300 Wh | 9.5 hours | 3.6 hours | 2.2 hours | 0.46 hour |
| 500 Wh | 15.8 hours | 6.0 hours | 3.7 hours | 0.76 hour |
| 1,000 Wh | 31.5 hours | 11.9 hours | 7.3 hours | 1.52 hours |
| 2,000 Wh | 63.1 hours | 23.8 hours | 14.7 hours | 3.03 hours |
What changes the result?
AC versus DC output
AC output uses an inverter, adding conversion loss and idle consumption. A compatible DC or USB load may avoid some of that loss, but cable and voltage-conversion losses still exist.
Continuous and cycling loads
A lamp may draw steadily, while a refrigerator cycles. Use measured daily energy or realistic average watts for a cycling appliance instead of treating nameplate watts as continuous.
Battery temperature and age
Cold conditions, heat exposure and normal aging can reduce available energy. Leave a reserve for critical loads instead of planning to the final minute.
Solar input
Solar can extend runtime, but it should not be treated as guaranteed power. Weather, shading, panel angle and the station’s charge-input limit all affect production.
Runtime on one charge versus battery lifespan
Runtime is how many hours the station powers a specific load before it needs charging. Battery lifespan is how long the battery retains useful capacity across repeated charge cycles and calendar aging.
Do not judge service life from chemistry alone. Check the manufacturer’s cycle-life specification and the capacity threshold attached to it—for example, a stated number of cycles until the battery reaches a certain percentage of original capacity. Storage temperature, time spent fully charged or deeply discharged, charge rate and operating heat can all affect long-term capacity.
A station does not normally become useless when it reaches the manufacturer’s cycle-life threshold. It usually stores less energy than it did when new, so the same appliance runs for less time.
How to get a more accurate estimate
- Find the station’s rated battery capacity in watt-hours—not only its maximum output watts.
- Measure the appliance with a plug-in power meter when possible.
- For motors and compressors, record both running watts and startup surge.
- Choose a realistic usable-capacity and efficiency assumption.
- Add the power station’s inverter idle draw.
- Test the real setup before depending on it during an outage.
If you do not know the appliance load, start with the Appliance Wattage Library. For a cycling compressor, use the dedicated Refrigerator Backup Calculator.
Calculate your exact setup
Enter battery watt-hours, running load, startup surge, inverter ratings, efficiency, usable capacity and idle draw for a more defensible estimate.
Frequently asked questions
How long will a 500 Wh portable power station last?
With the assumptions used in this guide, about 3.7 hours at a steady 100 W AC load, 6 hours at 60 W or 46 minutes at 500 W. Enter the real load and station settings for a better estimate.
How long will a 1,000 Wh power station run a TV?
If the TV and connected devices average 100 W, the worked example estimates about 7.3 hours. A lower-power TV may run longer; brightness, screen size and external devices matter.
Can a portable power station run a heater?
Some high-output stations can, but resistance heaters consume energy very quickly. Confirm the heater’s watts are below the continuous inverter limit and expect far shorter runtime than with electronics.
Should I size a station by watts or watt-hours?
Use both. Watts and surge watts decide whether the station can power the appliance; watt-hours determine approximately how long it can run.
Why did my station shut down before reaching zero?
Possible causes include overload, startup surge, low-temperature protection, battery-management reserve, thermal protection or a load that changed during operation. Check the station’s event code and manual.
Bottom line
Portable power station runtime is not one fixed number. It depends on the battery’s usable watt-hours and the real battery-side draw of the appliance. Calculate the load, conversion losses and idle draw separately, verify surge compatibility, then leave a safety reserve. For long-term ownership, compare cycle-life specifications as well as capacity and output power. New to the hardware? Read how a portable power station works. Still choosing the backup type? Compare a portable power station versus a fuel generator.