Guides

Calculator

Battery Runtime Calculator

Estimate how long your battery can run a steady load. Use your battery's nominal capacity and choose how far you plan to discharge it. For an AC load, enter your inverter's efficiency at that load.

Not sure what to enter? Read the step-by-step guide.

Your inputs

What gets replaced?

Compatible fields are replaced with values from your saved setup, including blanks. Capacity values and units are replaced together where supported. Other fields stay unchanged. You can undo the replacement until you manually change one of the replaced fields. Edit My Setup

Your battery
What does battery capacity mean?
Read the total battery bank rating in Ah or Wh from its label or documentation. Use the unit selected above; Ah also needs the bank’s nominal voltage.

Switching between Wh and Ah clears this value so it is not accidentally interpreted in the wrong unit.

What does battery level mean?
State of charge (SoC) is how full the battery is, expressed as a percentage.

Use the current reading from your battery monitor. The initial 100% is simply an example of a fully charged battery; imported values may differ.

What does minimum battery level mean?
This is the charge level where you plan to stop discharging the battery. The calculator does not assume a default based on battery chemistry.

Choose a limit appropriate for your battery and system based on the manufacturer’s or system guidance.

Your load
What does continuous load mean?
Continuous load is the power a device draws while running steadily. Use measured or documented input power. Do not enter a daily Wh total here.

All calculations run in this browser. Use running watts, not startup surge or a microwave's cooking output.

Runtime estimate

How long your battery could last

Your battery could run this steady load for

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Enter battery capacity, a minimum battery level, and a continuous load to see an estimate.

This is an energy estimate only. It does not confirm that the battery, battery management system (BMS), wiring, or inverter can safely supply the load. It excludes charging, temperature, aging, discharge-rate effects, and startup surge.

Edit your inputs
See calculation details, assumptions and sources

Nominal energy is the entered Wh, or Ah × nominal battery V. Available energy is nominal Wh × (current charge % − minimum battery level %) ÷ 100. For direct DC, divide available Wh by load W. For an AC load, the battery-side power demand is load watts ÷ inverter efficiency expressed as a decimal, for example, 80% = 0.8. Then divide available Wh by that battery-side power demand to estimate runtime in hours.

For example, a 12.8 V, 100 Ah battery has 1,280 Wh nominal energy. At 100% charge with a 20% minimum battery level, 1,024 Wh is in the selected range. A steady 100 W DC load gives 10.24 hours. At 80% inverter efficiency, a 100 W AC load draws about 125 W from the battery and gives 8.192 hours.

Choose the minimum battery level using your battery's guidance and condition. Capacity can change with discharge rate, temperature, and age. Inverter efficiency varies with load, and its idle use is not separately modeled here. A cycling load needs its own duty-cycle estimate; a daily Wh total is not a continuous W load.

References: Victron battery nominal V/Ah/Wh specifications, Victron on capacity and discharge rate, and Victron inverter efficiency and idle power specifications. See the site methodology.