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How long will my home battery run my house in a blackout?

Short answer. Divide the energy available in the battery (kWh) by how much power your home is using (kW). A battery with 10 kWh available, running a house using 1 kW, lasts about 10 hours; run a 3 kW load and it is about three hours. The number you actually get depends on the charge you had when the power went out, your reserve setting, what is running, and whether the sun is up.

Safety first. Never open a switchboard, remove a cover from your battery or inverter, or touch any wiring. Anything beyond the app, a light you can read from a safe distance, or your own router is a job for a licensed electrician. If you see smoke, smell burning, hear arcing or see water on or near the unit: keep everyone away, switch off at your main switch only if it is safe to do so, and call 000 if there is any fire or smoke.

The sum

Hours of backup are roughly usable kWh divided by average kW. This is an illustration, not a promise for your home:

  • Usable energy 10 kWh at an average load of 0.5 kW (fridge, lights, router) is about 20 hours.
  • The same 10 kWh at 2 kW (add a TV, kettle and some cooking) is about 5 hours.
  • The same 10 kWh at 5 kW (air conditioning, oven and a hot-water element) is about 2 hours.

Your power bill and app usage show your real averages: our free energy assessment reads them from your bills.

What changes the answer

  • How full it was: a battery at 40% when the grid fails has less to give than one at 100%. Backup Reserve keeps a floor for this: what is Backup Reserve?.
  • What is running: heating elements, air conditioners, ovens and EV chargers use far more than lights and a fridge. Leaving big loads off the backup circuits, or using them sparingly, stretches the charge.
  • Solar during the day: if the sun is up, solar can run the house and recharge the battery, so a daytime outage can last much longer than the arithmetic suggests.
  • Power limit (kW): every battery and inverter can deliver only so much power at once. A large combined load can trip the backup even when the battery has plenty of charge.
  • Whole home or essential circuits: a typical install of ours backs up the whole home unless you ask us to leave out circuits (an EV charger, for example). See whole home vs essential circuits.

How to stretch it in a long outage

  • Switch off big loads you do not need (air conditioning, oven, hot-water element, EV charger).
  • Check the app for the remaining charge now and then, if the app still works. See what if the app is offline?.
  • Use appliances one at a time rather than together.
  • If a storm is forecast, raise your reserve ahead of time. Tesla’s Storm Watch and SolaX’s Backup mode are examples of features built for this.

Read more: blackout backup batteries, what size battery do I need? and checking your Sigenergy backup. A battery cannot guarantee backup in every circumstance, and it is not suited to life-sustaining medical equipment without a separate plan.

When to call us

If we installed your system, call us on 0483 903 020. Our service help for existing customers is free: we start by working through it with you by phone. If you are not yet a customer, a service call is $250 + GST, which covers one hour on site within 20 km of Mullumbimby; travel further out is quoted separately. Contact us or call 0483 903 020 (Mon-Fri 7am-6pm, Sat 7am-4pm). We do not repair systems we did not install.

Quick questions

Can my battery run my air conditioner in a blackout?

Possibly for a limited time, but air conditioners draw a lot of power. It depends on the battery’s power limit, its charge and what else is running. Ask us about your system.

Does a bigger battery always last longer?

More stored energy lasts longer at the same load, but the power limit and your reserve settings still apply.

Will solar keep my battery topped up in an outage?

Often yes in daylight, if your system is set up to run on solar during an outage. That depends on the system and the weather.

How do I know my backup works?

Ask us about testing it safely; for Sigenergy owners see our backup check guide.

Sources

Last checked 7 October 2026. Only the manufacturer’s, the network’s or the government’s own documents are used; app menus and defaults change between models and versions, so if your screen looks different, call us rather than guess.

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