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  1. Home
  2. Units & math
  3. Battery backup runtime calculator
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Battery backup runtime calculator

Estimate how long a battery bank or UPS will run your load, or size a battery for a target runtime, with depth of discharge and Peukert options.

This tool is in beta

Still being tested. If a result looks wrong, tell us.

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Enter the bank and the load to see the backup time.

This is a steady-state estimate for one constant load. It does not model temperature, battery age, the inverter's idle draw, BMS cut-off voltage, or how a real load ramps up and down. Peukert's law is an empirical fit for lead-acid style chemistry, not a physical law, and the result is only as good as the datasheet figures you type in. Size critical systems with real headroom; nothing here replaces a commissioning test.

Battery, load, backup time

ChemistryPrefills depth of discharge and Peukert figures; edit them freely after
Use 100 for a DC load with no inverter
More settings▾
Leave empty to see the runtime; fill it in to size the bank
Worth applying to lead-acid style banks; lithium cells barely sag into it

The exponent goes above 1 and up to 3. The rated time is the C-figure on the datasheet: a C20 rating is 20 hours.

Series adds volts, parallel adds amp-hours. Numbers stay within ±1,000,000,000, targets up to 8,760 hours, rated times up to 240 hours.

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