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© 2026 WattQuick. All calculators are estimates—for planning only, not professional engineering advice.

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Backup

UPS Runtime

Estimate backup time from battery energy and load power.

Battery energyWh

Load powerW

Estimated backup time

Enter Wh and load watts

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About UPS Runtime

UPS runtime formula

Runtime (hours) = battery watt-hours ÷ load watts. This assumes constant load and ignores inverter efficiency—real runtime is often 10–20% shorter.

Finding battery Wh

Check your UPS specs for internal battery Wh, or multiply Ah × V. For a 12 V 42 Ah battery: 504 Wh.

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