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 a power cut, with the sums shown so you can check them.
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 care provider or equipment supplier.
Phones and tablets
From preppantry.app. Checked 2 November 2026. Independent tool, not official advice.
How it works
The sum 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 mains 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 fridge (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, not your appliance. Batteries hold less in the cold and as they age, and devices vary with what they're doing. Check the label on your own device and type its figure in.
Fridges and freezers. They switch themselves off once they're cold, so 150 W isn't what they use all day, and the real figure is lower. The list treats it as running non-stop, which makes the estimate on the short side. For a closer figure, enter the kWh per year from the fridge's energy label, and we'll work out its average. That figure comes from test conditions, so a warm room or an opened door will use more. Check the fridge's own label too: Generac lists a fridge at 700 W running and far more for a moment as the motor starts, so your station needs a surge rating high enough to start it.
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.
Why this matters in a power cut. The government's Be Ready campaign says that in the unlikely event of a national energy shortage, areas could be cut off for around three hours at a time on a rota. Most power cuts are short. If you live in a flat, a generator usually isn't an option, because it has to run outdoors, well away from windows and doors. A battery power station has no exhaust, so it can be used indoors. Follow its manual.
Common questions
How long will a 1,000 Wh power station run a fridge?
About 5.6 hours at the typical 150 W, on our estimate of 1,000 × 0.85 ÷ 150. Real fridges cycle on and off, so it could last longer. Enter the kWh per year from the energy label for a closer figure, and check the label for its start-up power too.
Can a power station run a kettle or heater?
Usually not for long. The Centre for Sustainable Energy lists a kettle at 3,000 W and an electric heater at 2,500 W. Check the station's maximum output first. If one could run a 3,000 W kettle, a 1,000 Wh battery would last about 17 minutes on the estimate.
Can I run a CPAP or other medical device from a power station?
Ask your care 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.
How do I work out watt-hours from mAh?
Multiply mAh by the voltage, then divide by 1,000. 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
- Be Ready: power cuts
- Priority Services Register
Contains public sector information licensed under the Open Government Licence v3.0.
Checked on 2 November 2026. This is an independent tool and not official advice. See sources and method.