Two numbers define the size window. The first is the 5 kWh floor. The second is the 100 kWh ceiling for eligibility, with STCs counted on up to 50 kWh.
The 5 kWh minimum
The program covers batteries from 5 kWh of usable capacity. A smaller unit, such as a compact 3 or 4 kWh backup battery, does not qualify for STCs. For customers who want a small battery, a 5 kWh unit sits at the bottom of the range and earns certificates on every kWh.
The 100 kWh maximum
Systems up to 100 kWh usable are within the program’s scope. But the number of STCs is capped by calculating on up to 50 kWh. A 75 kWh commercial battery is eligible, yet it earns certificates only on the first 50 kWh. Business buyers should factor this in; our page on business battery eligibility covers that angle.
How the tiers shape the number
Since 1 May 2026 the first 14 kWh counts at 100% of the factor, 14 to 28 kWh at 60%, and 28 to 50 kWh at 15%. The factor itself was 6.8 at the time of writing, stepping down to 5.7 on 1 January 2027 and 5.2 on 1 July 2027. That tiering is why bigger is not proportionally better. For a worked example, see the 14, 28 and 50 kWh tiers and which size gets the biggest rebate.
A quick illustration of the shape, using the 6.8 factor: a 10 kWh battery counts 10 kWh at 100%, while a 20 kWh battery counts 14 kWh at 100% and 6 kWh at 60%. The second is twice the capacity but well under twice the certificates. Use the battery STC calculator for exact numbers.
Remember that the factor itself steps down every six months, so the same battery earns fewer certificates later. At the time of writing it is 6.8, then 5.7 from 1 January 2027 and 5.2 from 1 July 2027. A customer deciding between sizes should also consider the date of installation.
What this means for installers
Record usable capacity from the CEC listing or datasheet and keep it consistent across the invoice, the form and the photos. A mismatch between the listed capacity and the claimed capacity is a trigger for queries. See the battery submission guide and battery photo guide.
What this means for homeowners
Do not buy for the biggest rebate; buy for your usage. The first 14 kWh gets the full factor, so most households find value in the 10 to 14 kWh range. For program background see battery STCs.
Installers can compare buy rates on pricing or start trading.