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Power Station Runtime Calculator
How long a portable power station runs your devices.
Free tools that run in your browser. Nothing you type, open or create is uploaded to NerdBible or anyone else.
Your devices
The device figures in the list are typical values, not measurements of your devices. The real draw is printed on the device or its charger (watts, or volts times amps), and a plug-in power meter shows it exactly. Fridges and freezers cycle on and off, so use their average draw, not the compressor's running figure. Devices with a motor or heating element can need two or three times their rated power for a moment when they start.
How to use it
- Enter the station's capacity in watt hours (Wh), from its spec sheet or label.
- Keep 85% inverter efficiency for devices on the AC sockets, or raise it to about 90 to 95% if everything runs from USB or 12 V outputs.
- Add your devices with their watts, how many you run and how many hours a day each is on.
- Read the runtime with everything switched on, and how many days a full charge lasts at your hours of use.
Questions
Why is the runtime shorter than capacity divided by watts?
Converting battery power to mains AC loses energy as heat in the inverter, typically 10 to 20%. Most stations also keep some charge in reserve to protect the battery. Both are taken off the capacity before dividing.
What should I enter for usable capacity?
The share of the rated capacity you can actually draw. Many lithium stations let you use 90% or more of the rated figure; the manual or a review that measured it will tell you. Lower it if you never run the battery fully flat.
What does max output mean?
The most power the station can deliver at once, in watts. If your devices together need more than that, the station will shut off however much charge is left, so the tool warns you.
Does the station drain when nothing is plugged in?
A little. An inverter that is switched on uses power even with no load, often 5 to 20 W, so switch AC off when you only use USB. Batteries also lose some charge slowly in storage.
Is this accurate enough to rely on?
It is an estimate for planning. Real runtime depends on temperature, battery age and how much each device really draws. Leave a margin for anything important.
About this tool
How long will a power station run my devices?
Portable power stations are sold by capacity in watt-hours (Wh). Your devices use power in watts (W). Divide one by the other and you have a rough runtime, but real results come in lower, and this calculator allows for why.
How the estimate works
- Enter the power station's capacity in Wh.
- Add each device with its power draw in watts, found on its label or charger, and how many hours a day it runs.
- The estimate takes off the energy lost converting battery power to mains AC through the inverter, typically 10 to 20 percent, and the reserve most stations keep to protect the battery, so it comes in below a plain division. Both figures can be changed.
For example, 1000 Wh feeding a 100 W load divides to 10 hours, but with the default 85 percent inverter efficiency and 90 percent usable capacity the estimate is about 7 hours 40 minutes. For appliances that cycle on and off, such as a fridge, use the average draw rather than the peak.
Tips for a realistic figure
Check the rated output too: a power station cannot start a device whose surge exceeds what its inverter can deliver, however much capacity is left. Devices charged over USB or 12 V skip the inverter and waste less. Cold weather reduces usable battery capacity, so allow extra margin for winter camping or outages.
All calculations run in your browser; nothing you enter is sent anywhere.
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