Battery Backup Calculator

Calculate how long a battery or UPS can power your devices based on battery capacity, voltage, and the total load connected.

Enter Values

Battery Capacity (Ah)

Battery Voltage (V)

Total Load (Watts)

Inverter Efficiency (%)

Enter values above and click Calculate to see your result.

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Runtime (hrs) = (Battery Ah × Voltage × Efficiency) ÷ Load (W)

Converts battery capacity (Ah × V) to watt-hours, applies efficiency loss, then divides by the connected load to find runtime.

150Ah battery, 12V, 85% efficiency, 500W load → (150 × 12 × 0.85) ÷ 500 = 3.06 hours.

Inverters lose 10-20% of energy as heat during DC to AC conversion. An 85% efficiency is a common real-world value.

Ampere-hours (Ah) measures battery capacity. A 150Ah battery can theoretically deliver 15 amps for 10 hours or 1 amp for 150 hours.

No. Deep discharging damages lead-acid batteries. Only use 50-60% of rated capacity for longevity. Lithium batteries can safely use 80-90%.

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