People often phrase this three ways: can I expand my battery and claim, can I add modules, and can I top up a battery I installed earlier. They are the same question, and the answer depends on one thing, which is whether the existing battery has already had the discount.
The rule in plain terms
Under the Cheaper Home Batteries Program, capacity added to an existing battery system can be eligible for a discount on the added capacity, provided:
- The existing battery system has not previously received a discount under the program.
- The additional capacity is at least 5 kWh nominal.
- The total capacity after the upgrade is no more than 100 kWh nominal.
- The new capacity is installed, commissioned and documented to the same standard as any other battery, by an accredited installer, with CEC-approved equipment that is VPP-capable.
Check the DCCEEW and Clean Energy Regulator pages for the current wording before you quote an expansion, because details have been tightened more than once.
Who this helps
The case that most often fits is a household that bought a battery before 1 July 2025 (so it could not claim) and wants to add capacity now. The first battery was never discounted, so the added modules can be. The case that does not fit is a battery that already received a discount: the one-per-premises rule applies and further capacity earns nothing. See second battery on the same property.
Adding modules in small steps
Small modules of 2 to 4 kWh do not meet the 5 kWh minimum on their own. If you want to add one, the choice is to wait and add 5 kWh or more in one go, or to add it knowing there is no STC value. Splitting a larger addition into two small visits to game the threshold would be a poor idea, and would be a compliance problem for the installer.
How the certificates are worked out
The added capacity is run through the same calculation as a new battery: usable kWh times the factor for the commissioning period, with the tiers. Because the existing battery already occupies some capacity, how the tier boundaries apply to expansions is a detail to confirm with the regulator. See nominal versus usable capacity and run an estimate through the battery STC calculator.
What this means for installers
Treat an expansion as its own job: new serial numbers, new photos, a new assignment form, and notes recording the existing system and its history. Our compliance desk pre-checks these claims before lodgement. See the battery submission guide and our battery STCs pillar, and if you want to move your battery claims to a partner with a named account manager, start at /start-trading/.
What this means for you
If you are planning an expansion, ask the installer to state in writing why the job is eligible and what the STC count assumes. Compare that with the factor schedule, since the 6.8 factor is scheduled to fall to 5.7 on 1 January 2027 and to 5.2 on 1 July 2027.