How long will your power station really last?
Pick your devices, enter your battery size, and get an honest runtime. Inverter loss, fridge cycling and surge limits are all included. Free, no sign-up.
On % is the share of time a device actually draws power. A fridge’s compressor only runs about a third of the time.
Ways to stretch your runtime
- Run big heating loads (space heaters, kettles, hair dryers) only when truly needed. They drain a battery in under an hour.
- Use DC and USB outputs when you can. Skipping the AC inverter avoids the 10–15% conversion loss.
- Pre-chill your fridge, then open it as little as possible. Keep it out of direct sun.
- Swap to LED lights and charge devices from USB-C instead of wall bricks.
- Add solar input during the day to refill while you use it.
Frequently asked questions
How is the runtime calculated?
We multiply each device’s watts by its quantity and its “on” percentage, then add them up for your average load. Runtime is battery watt-hours × inverter efficiency ÷ average load in watts.
What is inverter loss?
A power station converts its stored DC power to AC for your wall-style outlets, and some energy is lost as heat. Most units are 85–90% efficient, so a 1,000 Wh battery delivers roughly 850–900 Wh of usable AC power.
Why doesn’t a fridge use full power all day?
A fridge compressor cycles on and off to hold temperature. A full-size fridge might draw 150 W when running but only run about 35% of the time. That’s why we use a duty cycle instead of the label wattage.
What is surge (starting) power?
Motors in fridges, pumps and tools briefly draw 2–7 times their running watts when they start. If that spike plus your other loads exceeds your max output, the unit may shut off. The calculator warns you when this could happen.
Can I use my full battery capacity?
Not always. Many units shut down at 5–10% charge, and cold weather reduces capacity. Treat your result as a best case and keep a 10–20% buffer.
How do I find a device’s wattage?
Check the label near the power cord, or multiply volts × amps. A plug-in watt meter gives the most accurate reading. You can edit any number in the list.
Is this tool really free?
Yes. There’s no account, no sign-up and no limit. The site may show ads to cover its costs.
About
This calculator exists because most runtime tools are built by battery brands or ignore how appliances really behave. It is brand-neutral, simple, and made for people planning for outages, camping trips and van life.
It gives estimates, not guarantees. Real runtime depends on temperature, battery age, and how your devices behave. Always keep a margin for safety, especially for medical equipment.
Contact
Privacy policy
Last updated: November 12, 2026
The calculator runs entirely in your browser. The devices, wattages and battery sizes you enter are not sent to us or stored on a server. We don’t require accounts and we don’t ask for personal information to use the tool.
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