How to use it
- Start from the list we've already filled in: a typical outage setup with the fridge, internet, lights, phones and a laptop. Remove anything you won't need.
- Add more from the dropdown, or choose "Custom" and type in the watts from the appliance label.
- Be realistic about hours. A fridge compressor only runs about a third of the time, so 8 hours covers a full day. A microwave runs for minutes, not hours.
- Pick how many days you want to last without recharging. Most people plan for one and top up with solar or the car.
The two numbers that matter
Every power station has two ratings, and you need enough of both. Capacity, in watt-hours, is the size of the fuel tank: it decides how long things run. The calculator takes your daily use, multiplies it by the number of days and divides by 0.85 to cover conversion losses.
Output, in watts, is the size of the engine: it decides whether something can run at all. Plug in more than the inverter can handle and the unit shuts itself off, however full the battery is.
Anything with a motor or compressor, like a fridge, freezer, pump or AC, briefly pulls two to three times its running watts when it starts. That's the surge figure, and the power station's surge rating has to cover your running load plus the biggest of those start-up spikes.
Typical results
| Scenario | Daily energy | Power station class |
|---|---|---|
| Phones, router, a few LED lights | ~700 Wh | 1,000 Wh |
| CPAP for one night | ~350–750 Wh | 500–1,000 Wh |
| Fridge + router + lights + phones | ~2,100 Wh | 2,500–3,600 Wh |
| Fridge + freezer + sump pump + essentials | ~4,500 Wh | 5,000 Wh+ (expandable) |
| Window AC overnight + essentials | ~6,500 Wh | Expandable home battery or generator |
Making a smaller power station go further
- Keep the fridge closed and fill the empty space with water bottles. The extra mass keeps the compressor off for longer.
- Use the DC outputs (USB-C, 12 V) for phones, laptops and CPAPs. Skipping the inverter saves 10–15%.
- Cook outside on gas or propane instead of using the microwave or kettle. Anything that heats drains a battery fast.
- Add solar. Even 200 W of panels can put back 600–900 Wh on a sunny day, and the solar charge time calculator will help you plan it.
To see how long a specific unit would last, try the runtime calculator, or look up any device in the appliance wattage chart.