12V Install Tools & Testers

Battery Runtime Calculator

Estimate how long a battery or portable power station will run a steady load, from its amp-hour or watt-hour rating.

This gives an idealised runtime estimate for one steady load, or the average of loads that cycle on and off. It works for a battery (Ah) or a portable power station (Wh). Everything is worked out in your browser. Nothing is saved or sent anywhere.

1. Your battery or power station

Use the rated capacity from the label or manual. For a power station, use its watt-hour (Wh) rating.

Used to turn Ah into Wh, and for the current estimate.
Use the maker's recommended depth of discharge. Our battery size calculator uses 80% for lithium and 50% for AGM, flooded and gel as starting points.

2. Your load

Enter the load's power in watts. For something that cycles on and off, such as a compressor fridge, use its average draw over the day, not the peak on the label.

Only used for AC loads. Check your inverter or power station manual.

3. Results

How it was worked out

    What this does and doesn't tell you

    • This is an idealised estimate for a constant load. Real runtime is usually shorter, and it varies with battery age, temperature, discharge rate, low-voltage cut-off and the battery management system.
    • It does not model start-up surge, or the way lead-acid and AGM capacity falls at higher discharge rates.
    • Inverter standby (no-load) power isn't included. If the inverter stays on, add its standby watts to the load. Power stations also draw some power to run their own inverter and screens.
    • Running several loads? Add up their average watts, or work out your daily energy use with the Daily Energy Use & Battery Size Calculator.
    • Work on 240V AC wiring, including inverter outputs and mains inlets, must be done by a licensed electrician. For high-current DC gear such as inverters, DC-DC chargers and battery links, follow the maker's installation manual and have an auto electrician check your work if you're unsure.

    Next steps

    Size a battery for everything you run each day with the Daily Energy Use & Battery Size Calculator, then check how much solar or DC-DC charging you need with the Solar & Charging Check and the DC-DC Charger Size Calculator. To see how long recharging takes, use the Battery Charging Time Calculator. Building a bank from several batteries? Use the Battery Bank Series & Parallel Calculator. Weighing up an all-in-one unit? Read Power Station vs DIY Battery Box and Lithium vs AGM Battery for Camping.

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