The short answer
Size your battery to what you use in the evening and overnight, not your whole day. Many homes are well served by 10 to 15 kWh; homes with an EV, electric heating or a big evening load often go larger. The rebate pays most on the first 14 kWh, so capacity beyond 28 kWh costs you much more per kWh.
Start with your evenings
During the day your solar runs the house. A battery covers what comes after: dinner, lights, TV, air-con or heating, and whatever runs overnight. That evening and overnight use is what to size it to.
Your retailer's online account shows your use by time of day. If you have that, we can size your battery to it exactly.
What changes the answer
- An EV charged at home overnight can need 10 kWh or more on its own
- Electric heating, a heat pump or induction cooking add to evening use, especially in winter
- Backup in a blackout: the more you want to keep running, the more you need in reserve
- Your solar: a battery needs enough spare solar to fill it each day
- Single-phase or three-phase power, which decides which batteries suit
How the rebate changes it
The rebate pays the full rate on the first 14 kWh, 60% of it from 14 to 28 kWh, and 15% from 28 to 50 kWh. Capacity past 28 kWh costs you much more per kWh, so only go that big if you'll really use it.
The average new home battery was 26.6 kWh in June 2026, so many people are going big. That suits some homes and not others.
| Usable capacity | Installed by 31 December | Installed from 1 January | Difference |
|---|---|---|---|
| 10 kWh | $2,500 | $2,110 | $390 |
| 13.5 kWh | $3,380 | $2,850 | $530 |
| 16 kWh | $3,800 | $3,210 | $590 |
| 20 kWh | $4,400 | $3,720 | $680 |
| 28 kWh | $5,600 | $4,730 | $870 |
| 40 kWh | $6,050 | $5,120 | $930 |
Usable capacity is what counts
A battery's usable capacity is what you can actually draw from it, and it's what the rebate is worked out on. Compare batteries on usable capacity, not total.
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