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UPS runtime

Runtime is usable watt-hours divided by the load. Usable watt-hours are the battery capacity times inverter efficiency. A VA rating is not a watt rating: a PC supply with active power-factor correction still needs VA at least equal to watts divided by that power factor.

The opening example is 400 W into a 90 Wh battery at 85% efficiency. Replace both with the label on your unit. Runtime is not a battery-health test.

Estimated runtime

11 min

76.5 Wh reach the PC after the inverter assumption. Battery Wh is 90.0.

Required VA at this power factor421 VA
Suggested watt rating600 W
Suggested VA rating450 VA

The suggested size adds 25% above the watt load so the UPS is not specified at its ceiling. That headroom is a planning rule, not a measurement.

Estimates only. Use at your own risk.