PrepPower station runtime calculator
Enter your battery's size and what you'd run from it. You'll get an estimate of how long it lasts in an outage, with the math shown so you can check it.
Your battery
What would you run?
Typical watts. Check the label or plate on your own device and change the figure.
Medical devices: we don't list a figure for a CPAP, oxygen concentrator or any other medical device, because they differ. Check the device's own label. If someone relies on powered medical equipment, talk to your medical provider or equipment supplier.
Phones and tablets
From preppantry.app. Checked 2 November 2026. Independent tool, not official advice.
How it works
The math is hours = watt-hours × 0.85 ÷ watts. Watt-hours (Wh) are the size of the battery. Watts are what you're running. The 0.85 allows for what's lost turning battery power into household power. It's a rule of thumb from battery makers, with no official source, and your own station may do better or worse.
Example: a 1,000 Wh power station running a refrigerator (150 W) and a router (10 W). That's 1,000 × 0.85 ÷ 160, or about 5.3 hours.
Treat the answer as an estimate. The wattages are typical figures from the Centre for Sustainable Energy, a UK charity. US appliances can differ, and batteries hold less in the cold and as they age. Check the label on your own device and type its figure in.
Refrigerators and freezers. They switch themselves off once they're cold, so they don't draw their rated watts all day. The list treats 150 W as running non-stop. Figures vary a lot, though: Generac lists a refrigerator at 700 W running and far more for a moment as the motor starts, so check your refrigerator's own label, and check that your station's surge rating can start it. For a closer average, enter the kWh per year from the yellow EnergyGuide label. That figure comes from test conditions, so a warm room or an opened door will use more.
Power banks. If yours shows mAh rather than Wh, multiply the mAh by the voltage on its label and divide by 1,000. A 10,000 mAh pack marked 3.7 V is 37 Wh. Enter the voltage from the label, because some packs are rated differently.
Power station or generator? A battery station has no exhaust, so it's the one to use indoors. Follow its manual. A generator runs longer but must stay outdoors, because of carbon monoxide. Our generator size calculator covers that, with the safety rules first.
Common questions
How long will a 1,000 Wh power station run a refrigerator?
About 5.6 hours at a typical 150 W, on our estimate of 1,000 × 0.85 ÷ 150. Real refrigerators cycle on and off, so it could last longer, but larger models can draw much more. Enter the kWh per year from the EnergyGuide label for a closer figure, and check the label for its power use.
Can I run a CPAP or other medical device from a power station?
Ask your medical provider or equipment supplier first. We don't give a figure, because devices differ. Check the device's own label, and enter that figure if you want an estimate, but don't rely on it alone.
Can a power station run a microwave?
Only if its maximum output is above the microwave's rating. Generac and the Centre for Sustainable Energy both list a microwave at 1,000 W. On the estimate, a 1,000 Wh battery would run it for about 51 minutes in total.
How do I work out watt-hours from mAh?
Multiply mAh by the voltage, then divide by 1,000. The FAA gives the same steps for lithium batteries. If the case shows watt-hours, use that number.
What's the difference between Wh and W?
Wh is how much energy the battery holds. W is how fast something uses it. A station also has a maximum output in watts: what you plug in can't add up to more than that, however large the battery is.
Sources
- Centre for Sustainable Energy: how much electricity am I using? (average power ratings, reviewed July 2026)
- Generac: GP series brochure (refrigerator running and starting watts)
- FAA PackSafe: working out watt-hours
- Ready.gov: power outages
Checked on 2 November 2026. This is an independent tool and not official advice. See sources and method.