What size battery do I need?
The short answer
Battery size starts with your quarterly power bill. The fit check starts at 9 kWh for a bill under $300 or $300 to $600, 18 kWh for $600 to $1,000 and 27 kWh for over $1,000. On single phase, the battery gets a 10 kW hybrid inverter. Budget, phase and when you use power can change it.
. Written by Nick Green.
Start with your power bill
Your quarterly power bill is a rough guide to how much electricity you use. The fit check uses it as the first step in choosing a battery size. This table shows the starting size for each bill band, before anything else is taken into account.
| Power bill each quarter | Starting size |
|---|---|
| Under $300 | 9 kWh |
| $300 to $600 | 9 kWh |
| $600 to $1,000 | 18 kWh |
| Over $1,000 | 27 kWh |
Sizes come in steps, so the fit check rounds to a real product size.
Battery sizes are given in kilowatt hours (kWh). A kWh is the unit of energy on your power bill.
Sizes come in steps
Batteries are sold in set sizes, so the fit check rounds to a real product size: 9, 18, 27, 36, 45 and 54 kWh.
What can move the size
- Your budget. If you plan to spend more, the fit check will not suggest less than 18 kWh. Most of the federal discount applies up to 14 kWh, so going smaller leaves some of it unused.
- Your phase. A three phase home with a very high bill may be sized larger.
- Your own habits. A table cannot see when you use power. Your actual bill can.
Why the inverter matters
An inverter changes the direct current from your solar panels and battery into the alternating current your home uses. A hybrid inverter does that job for both.
On single phase, the fit check pairs the battery with a 10 kW hybrid inverter rather than a smaller one. Your home's own load and the charging of the battery can add up to more than a small inverter can carry. On three phase, the range is 10 to 15 kW.
What each size costs
These are the price bands for a battery installed with a new hybrid inverter. A battery size with no band shown is one where Nick confirms the price at the consult.
| Battery size | Single phase | Three phase |
|---|---|---|
| about 9 to 10 kWh | $11,000 to $11,500 | $12,000 to $13,000 |
| about 13 to 14 kWh | Nick confirms this price at the consult. | Nick confirms this price at the consult. |
| about 16 to 20 kWh | $14,000 to $14,500 | $14,500 to $16,000 |
| about 25 to 28 kWh | $17,500 to $18,000 | $18,000 to $19,500 |
| about 36 to 40 kWh | $21,500 to $22,500 | $22,500 to $24,000 |
| about 45 to 54 kWh | $26,000 to $31,500 | $27,000 to $33,000 |
These are our installer partner's current cash prices, installed, after the federal battery discount at the rate now in force. Prices include GST. They do not include any travel charge for your area.
Last checked 29 Sep 2026.
Here are two of the bill bands above with the price band for their starting size.
$300 to $600 a quarter
Starting size 9 kWh. Price band: about 9 to 10 kWh.
- Single phase
- $11,000 to $11,500
- Three phase
- $12,000 to $13,000
These are our installer partner's current cash prices, installed, after the federal battery discount at the rate now in force. Prices include GST. They do not include any travel charge for your area.
Last checked 29 Sep 2026.
Over $1,000 a quarter
Starting size 27 kWh. Price band: about 25 to 28 kWh.
- Single phase
- $17,500 to $18,000
- Three phase
- $18,000 to $19,500
These are our installer partner's current cash prices, installed, after the federal battery discount at the rate now in force. Prices include GST. They do not include any travel charge for your area.
Last checked 29 Sep 2026.
What to do next
The fit check takes your budget, your phase and the rest of your answers into account and gives you one suggested size. To see how the federal discount changes with size, read the guide to the federal battery discount. If you are still deciding whether a battery suits you at all, read whether a home battery is right for your home.
Common questions
Is a bigger battery always better?
No. A bigger battery costs more, and the federal discount pays less for each extra kWh above 14 kWh. The right size is the one that fits how you use power, not the largest you can afford.
How do I know if I have single phase or three phase?
Look in your meter box. One main switch usually means single phase, and three main switches usually mean three phase. An installer confirms it on site, and not sure is a fine answer on the fit check.
Why a 10 kW inverter on single phase?
The inverter has to carry the load of your home and the charging of the battery at the same time. A smaller inverter can hold that back. This is what the fit check recommends, and an installer checks it on site.
Does the price include installation?
Yes. The price bands are for an installed system, with GST included and after the federal discount. They do not include any travel charge for your area.
Check what fits your home
The fit check asks a few short questions and gives you a suggested size, a price range and the federal battery discount worked out for your home. Nick only calls if you ask him to.
Start the fit checkThis site is run by Nick Green, a solar and battery adviser who works with a licensed installer partner. We do not compare installers. If your home is a good fit and you ask us to, Nick will call you and prepare a quote through that partner. No cold calls, no door knockers, no obligation.
Where the facts come from
These are the official pages behind the rules and figures on this page. Read them yourself if you want to check us.
- DCCEEW: Cheaper Home Batteries Program (page last updated 9 June 2026)
- DCCEEW: Small-scale technology certificates for batteries (page last updated 9 July 2026)
Last checked 29 Sep 2026
Keep reading
Is a home battery right for your home? (NSW and QLD, 2026)
Who a home battery may suit, what decides whether it works for you, and the questions to ask before you agree to anything. Written for NSW and Queensland homes.
The federal Cheaper Home Batteries discount explained, with worked examples
How the federal Cheaper Home Batteries discount, often called the battery rebate, is worked out, why each extra kWh earns less, and worked examples to check.