What a battery actually keeps running.

The 30-second take

• A battery without backup wiring still shuts down in a blackout — it saves money, not lights.
• Essential-circuits backup keeps a nominated set of circuits live. It is the most common option.
• Whole-home backup keeps everything live but costs more and can still trip on heavy loads.
• Air conditioning, ovens, and electric hot water are the loads most likely to be excluded.
• Compare battery quotes on backup scope and usable kWh, not on headline price.

The three levels of backup

Backup is not a yes/no feature. It is a scope decision, and the scope drives both the price and the switchboard work involved.

• No backup. The battery charges from surplus solar and discharges in the evening to cut your bill. In an outage it shuts down with the rest of the system. Cheapest, and perfectly sensible if bill savings are the goal.
• Essential circuits. A nominated backup circuit keeps chosen loads live — typically the fridge, some lighting, and a few power points for phones and internet. Requires switchboard work to separate those circuits.
• Whole-home backup. The entire installation stays live during an outage. More switchboard work again, a higher-capacity inverter, and a real possibility of overload if everything runs at once.

What realistically runs, and for how long

Two numbers decide this: the battery’s usable capacity in kilowatt-hours, and the continuous power output of the backup-capable inverter in kilowatts. Capacity determines how long; power output determines what can run at the same time.

A fridge, LED lighting, wifi and device charging together draw a modest continuous load, which is why they are the standard essential-circuits selection — a typical home battery can carry them for many hours. Heating and cooling, ovens, and electric hot water draw many times more, and are usually excluded regardless of capacity.

• Usable kWh, not nameplate. Compare batteries on usable capacity — it is also what the federal rebate is calculated on.
• Continuous vs peak output. Some appliances draw a large surge on start-up. An inverter that handles the running load may still trip on the surge.
• Solar recharges the battery during a daytime outage, if the system supports it — which meaningfully extends how long you last in a multi-day event.

“Capacity decides how long you last. Inverter output decides what you can switch on at once. Quotes usually advertise the first and stay quiet about the second.”

What backup adds to the price

Backup is not just a setting. It is a separate backup circuit, often a switchboard upgrade, and sometimes a different inverter — which is why the same battery can appear in two quotes thousands of dollars apart.

That gap is frequently mistaken for one installer being expensive. Often it is one quote including backup and the other not. Establish scope before comparing totals.

Questions that make two quotes comparable

• Which specific circuits stay live in an outage? Ask for them listed on the quote, not described verbally.
• What is the usable capacity in kWh, and what is the inverter’s continuous backup output in kW?
• Does the system recharge from solar during an outage, or only from the grid?
• Is a switchboard upgrade included, and if not, what would it cost?
• How does it switch over — is there a brief interruption, and does anything need resetting afterwards?

Give every installer the same brief on capacity and backup scope and the quotes become genuinely comparable. Get matched with 2-3 vetted installers and compare on that basis.

Read next

• Do solar panels work in a blackout?
• How solar batteries work
• Solar battery cost in Australia
• The Cheaper Home Batteries Program explained
• Home batteries and storage

Sources

• standards.org.au — AS/NZS 4777.2 grid connection of energy systems via inverters
• cleanenergycouncil.org.au — buying solar
• uts.edu.au — CER battery inspection findings, April 2026