Usable capacity (battery)

Written and checked by the Energy Merchants desk · Reviewed 2 October 2026

Usable capacity is the energy a battery can actually deliver, measured in kilowatt-hours (kWh). Batteries hold back some of their total energy to protect cell life, so the usable figure is smaller than the headline one.

Under the Cheaper Home Batteries Program, which started on 1 July 2025, STCs are created for eligible batteries between 5 and 100 kWh usable, with up to 50 kWh counted. The STC factor, 6.8 per kWh for 2026 installs and stepping down to 5.7 on 1 January 2027 and 5.2 on 1 July 2027 (the factor now steps every six months to 2030), is multiplied by usable capacity.

Worked example

A battery with 10 kWh usable capacity installed in 2026 creates 10 x 6.8 = 68 STCs. At roughly $38 to $40 per STC at the time of writing, that is about $2,580 to $2,720. The same battery installed after 1 January 2027, at a factor of 5.7 (5.2 from 1 July 2027), creates 57 STCs.

In practice

Look for the usable figure on the product’s approved listing and datasheet, and use that number on the claim. Quote documents, brochures and online listings often show the nominal figure because it is bigger. If the claim and the product listing disagree, the claim will be questioned.

Stacked or modular systems need care. Add the usable capacity of each module as listed and make sure the photos show every unit and its serial number. Our battery submission guide covers the evidence, and the Cheaper Home Batteries Program installer guide covers eligibility.

Common confusion

Usable capacity and nominal capacity are different numbers for the same battery, and only one counts. See nominal capacity. Usable capacity is also not the same as power rating. A battery’s kilowatt (kW) rating says how fast it can charge or discharge. Usable capacity, in kWh, says how much energy it holds.

For the claim process, see battery STCs. Other terms are in the certificate trading glossary.