Battery Runtime Calculator

How it is calculated

The tool first finds the energy you can actually use: usable Wh = capacity (Ah) × voltage (V) × DoD / 100. Depth of discharge (DoD) is entered as a percentage, so 50 means half of the battery. Runtime is then hours = usable Wh / load (W) and minutes = hours × 60. The load must be above zero. The calculation assumes a constant load and a constant voltage, and it does not subtract inverter or converter losses, cable losses, or the capacity lost at high discharge currents or in cold weather. In practice, the real runtime is usually somewhat shorter than the figure shown, so leave a safety margin.

Common mistakes

• Entering the depth of discharge as a decimal such as 0.5. The field is a percentage, so 0.5 means half of one percent and the runtime comes out at minutes instead of hours; type 50.
• Mixing up battery voltage and inverter output voltage. Use the battery's own voltage (12, 24, 48 V), not the 230 V or 120 V of the appliance.
• Entering milliamp-hours (mAh) as Ah. A 5,000 mAh battery is 5 Ah, so divide by 1,000 first.
• Using the appliance's maximum power rating as the load when it normally draws less, or using its average when it has high starting surges. Use the realistic continuous watts.
• Ignoring conversion losses. Running a 230 V device from a battery through an inverter uses more power than the device label states, so the real runtime is shorter.