Home battery backup in a blackout: what it runs, for how long, and what to ask for

Why does solar stop working in a blackout?

Grid-connected solar is designed to shut down the moment the grid goes down, so it can't send power into lines that crews are repairing. That applies with or without a battery: a standard battery system also stops. Backup works by disconnecting your home from the grid first, then running it as its own small island from the battery, and the panels too if the system allows it.

What does a battery need to provide backup?

• A backup-capable inverter or gateway. Some batteries build it in; others need a separate unit, such as a gateway that isolates the home from the grid.
• Backup wiring. Usually a separate backup circuit board in or beside your switchboard, holding the circuits the battery will keep running.
• Commissioning. The installer has to set the system up for backup and test it. Ask to see the switchover tested on the day.

Some installers include this in a battery quote; others price it as an extra; some batteries can't do it at all. Comparing a quote with backup to one without isn't comparing like with like. More on comparing batteries: how to choose a home battery.

Essential circuits or whole-home backup?

Essential circuits is the common setup: the fridge, lights, wifi and a few power points stay on, and big loads such as ducted air conditioning, ovens and hot water don't. It keeps the battery going longer and needs less hardware. Whole-home backup keeps every circuit live, which is more convenient but drains the battery faster, and the battery's power rating (kW) has to cover everything you switch on at once. If you choose whole-home, check the continuous kW, not just the kWh: see kW vs kWh.

How long will a home battery last in a blackout?

Divide the stored energy (kWh) by what's running (kW). The table uses example loads; your fridge, your evening and the season change it. A full battery with nothing else coming in:

Two things shorten it. First, the battery is rarely full when the power goes: overnight it's been running the house. Homerise's sizing keeps 20% of the battery aside for blackouts, and most batteries let you set a reserve like that in their app. Second, if the battery is in a virtual power plant, an event can draw it down; check whether the VPP respects your reserve before you join (see virtual power plants).

Will your solar recharge the battery during a long outage?

On many backup systems, yes: once the home is islanded, the panels can keep charging the battery by day, which turns hours of backup into days. On others they stay off until the grid returns. It depends on how the solar connects. Panels on the battery's own hybrid inverter usually can; an older, separate solar inverter often can't unless the backup system is designed for it. If you're adding a battery to solar you already have, ask this question directly: adding a battery to existing solar.

How quickly does backup switch on?

Some systems switch so quickly that clocks and computers don't notice; others drop out for a few seconds up to about a minute while they detect the outage and island the home. If a short gap matters to you (a home office, a medical device, a fish tank pump), ask for the switchover time in writing.

What does backup add to the price?

The battery itself is the big cost: a 15 kWh battery is about $9,000 to $14,500 installed after the federal battery rebate (October 2026), and the rebate takes about $3,663 off that size (as of 22 October 2026). The backup hardware and wiring sit on top, and they vary with the battery, your switchboard and how many circuits you back up. Ask for backup as its own line in the quote so you can see it. A battery bought mainly for backup can still cut your bill every day it isn't needed: see is a home battery worth it. Planning an electric car too? See charging an electric car with solar.

Home battery, portable power station or generator?

• Portable power stations plug in where you need them and run a few devices. They don't connect to your switchboard or solar, and they don't get the federal battery discount, which applies to approved batteries installed by an accredited installer.
• Generators run for as long as you have fuel, but must only connect to the house through a changeover switch fitted by a licensed electrician. Never plug one into a power point.
• A home battery with backup switches over on its own, runs the circuits you chose, and earns its keep on your bill the rest of the year.

If anyone in your home relies on life support equipment, register it with your electricity retailer whether or not you have a battery: a battery is not a substitute for that.