Battery Essential-Load Duration Calculator
Estimate home-battery essential-load hours and inverter peak margin from usable kWh, state of charge, reserve and load.
Your results
Calculation breakdown
- Backup duration
- usable kWh × (starting SOC − reserve SOC) ÷ average load kW
Worked example
A 13.5 kWh usable battery from 80% down to 20% provides 8.1 kWh, running a 0.9 kW average load for nine hours with 0.5 kW peak margin.
Assumptions
- Usable capacity is defined before the entered SOC window.
- Average load remains stable without solar recharge.
Sources
Rates effective 23 August 2026.
How this calculator works
Estimate outage duration for selected essential loads from battery usable capacity, starting state of charge and reserve state of charge. Energy duration and inverter peak-power margin are shown separately because adequate kWh does not guarantee adequate kW. The calculation exposes its units and intermediate assumptions so Australian users can reconcile the estimate with bills, meters, labels, design records or site measurements.
Frequently asked questions
What should I measure for the battery essential-load duration result?
List actual essential loads, measure their average and starting demand, and confirm the battery is configured for islanded backup. Keep the measurement period and unit basis consistent across every input.
What can make this battery essential-load duration estimate differ?
Solar recharge, load cycling, battery ageing, temperature, conversion loss, surge duration and automatic load shedding are excluded. Recalculate with measured operating data before making a purchase, design or reporting decision.
Does this battery essential-load duration calculator confirm compliance?
No. It provides a transparent planning calculation only. For this topic, list actual essential loads, measure their average and starting demand, and confirm the battery is configured for islanded backup. Obtain qualified advice where electrical, plumbing, building, safety or reporting obligations apply.
Actual prices, usage, efficiency and savings vary by provider, equipment, location and behaviour.