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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.