Home battery runtime calculator
Pick a real battery setup, tick what you want to run, and see how long it lasts from full. Battery figures come from manufacturer datasheets; appliance figures are typical estimates you can change.
Average draw 156 W from 12.83 kWh available.
Everything on at once: 415 W — within the 11.04 kW limit
- Starts from a full battery with 0% held back as reserve.
- 5% extra allowed for wiring and standby losses on top of the manufacturer's usable figure.
- Appliance figures are typical averages; your own may differ. Enter your own wattage for the most accurate result.
- Assumes no solar recharging during the outage.
How the calculation works
Runtime = energy available ÷ average draw. Energy available is the manufacturer's usable capacity, minus any reserve you keep back, minus 5% for wiring and standby losses. Average draw adds up each appliance's wattage × the share of time it's actually drawing power. We also check whether everything you've ticked can run at the same time within the battery's continuous power limit.
Questions people ask
How long will a 10 kWh battery last?
It depends on what you run. Essentials only (fridge-freezer, lights, Wi-Fi, TV, device charging) average roughly 150–300 W, so a 10 kWh battery lasts roughly 30–60 hours. Add a heat pump in winter and it can drop to a few hours. Use the calculator with your own appliances.
Why is runtime different from capacity ÷ appliance wattage?
Fridges and heat pumps cycle on and off, so their average draw is lower than their rated wattage. We also allow for small wiring and standby losses and any reserve you keep back.
What is continuous power and why does it matter?
It's the most the battery can supply at once. If everything you switch on adds up to more than this, the system can't run it all together, even if there is plenty of energy stored.
Batteries in this calculator
Tesla Powerwall 3
An all-in-one home battery with a built-in solar inverter. One unit stores 13.5 kWh and can be expanded with up to three Expansion units.
Sigenergy SigenStor
A stackable system: a Sigen Energy Controller (hybrid inverter) with 1–6 battery modules of 5.2 or 7.8 kWh usable each.
Fox ESS EVO 10
An all-in-one battery and hybrid inverter with 10.24 kWh of LFP storage, sold in 5, 8 and 10 kW versions. Up to three units can run in parallel.
Enphase IQ Battery 5P
An AC-coupled 5 kWh battery with six built-in microinverters, so it can be added to most existing solar systems. Up to seven can be combined in the UK.
myenergi libbi
A UK-designed modular battery with a 3.68 kW or 5 kW hybrid inverter and 1–4 battery modules (4.6 kWh usable each). Built to work with myenergi's zappi and eddi.