How to read a solar battery quote (and spot a weak one)

Two quotes for "a 10 kWh battery" can differ by thousands of dollars and still both be fair — or one can be quietly worse in ways the headline number hides. If you've got a quote or three in front of you, here's what actually matters, line by line.

Compare usable capacity, not the headline number

A battery's headline size is its nominal capacity — the total in the cells. What you can actually draw each day is the usable capacity, which is lower, because no battery is run flat to protect its life. One quote's "13.5 kWh" and another's "13.5 kWh" can deliver different usable energy.

Always compare the usable kWh — that's the number that fills your evening. If a quote lists only the nominal figure, ask for the usable one.

Read the whole warranty, not just the years

"10-year warranty" is the start of the question, not the answer. Three things sit underneath it:

• Throughput — the total energy (in MWh) the warranty covers. A battery cycled hard can hit its throughput cap before ten years are up.
• Cycles — how many full charge and discharge cycles are covered.
• End-of-warranty retention — the capacity it's guaranteed to still hold at the end, often around 70%. Higher is better.

A longer year figure with a low throughput cap can be worth less than a shorter one with generous throughput. Compare all three.

Check round-trip efficiency

Every battery loses a little energy storing and releasing it. Round-trip efficiency — typically around 90% for a good lithium battery — tells you how much. An 85% battery quietly wastes more of your solar than a 95% one, every single day. It's a small number with a long tail.

Make sure it fits your existing solar

If you already have panels, how the battery connects matters:

• A hybrid inverter replaces your existing solar inverter and runs both the panels and the battery.
• An AC-coupled battery brings its own inverter and sits alongside your current one.

Neither is wrong, but they price differently and suit different setups. A good quote explains which it is and why it fits your system.

Know what "backup" actually means

If blackout backup matters to you, get specific. Some batteries back up your whole home; many back up only essential circuits — the fridge, lights and a few power points. Some need an extra component to provide any backup at all. "Backup ready" on a quote can mean very different things, so ask exactly what keeps running, and for how long.

Compare price like for like

The cheapest total isn't automatically the best value. To compare fairly:

• Look at price per usable kWh, not just the total.
• Confirm the price is after rebates, and which rebates are included — the federal STC rebate and the WA Battery Scheme are claimed differently.
• Check what the install includes. Switchboard upgrades, meter changes, mounting, monitoring and removal of old gear are sometimes extra.

Two quotes only compare honestly once they cover the same scope.

Check who's standing behind it

A battery is only as good as the support behind the warranty. Make sure the installer is SAA-accredited, that both the product and the workmanship are warranted, and that the brand has genuine Australian support — a warranty is worth little if there's no one local to honour it.

Put your quotes side by side

The fastest way to compare the products in your quotes on equal terms — usable capacity, warranty, efficiency, chemistry — is the comparison tool. It pulls specs from CEC and manufacturer data, so you're not relying on a single salesperson's word. When you want fresh quotes to weigh against the ones you have, request them from verified Perth installers in one go.

This is general guidance to help you evaluate quotes, not a recommendation of any specific product or installer. Always confirm specifications and warranty terms in writing before you buy.