The short version is that the federal discount is a one-off for each property. That shapes how you should size and stage a battery.
One battery installation per premises
The program rules limit the discount to one battery installation at a premises. It does not matter whether the second battery is a different brand, a bigger unit, or installed years later. Once a battery at that address has earned STCs, a second installation does not.
This also answers the “claim it twice” question. You cannot lodge two separate discounted installs and receive the discount on each.
What the rule does not stop
- A single system built from several units. A battery system installed together can be made of more than one module or cabinet. The capacity is added up and the certificate count is worked out on the combined system, with the tiers applied once. See two 13.5 kWh Powerwalls.
- A different property. The limit is per premises, so a holiday home or investment property is its own case; see holiday and second homes.
- Expanding a battery that never received the discount. Added capacity of at least 5 kWh can qualify if the existing system has not previously been discounted. See expanding an existing battery.
How to plan around the rule
Because you only get one bite, the useful question is how much capacity to buy now. The tiers matter: the first 14 kWh earns 100% of the factor, the next 14 kWh earns 60%, and 28 to 50 kWh earns 15%. Adding capacity later does not earn certificates, so a household that expects an electric vehicle or a bigger load may want to install the larger size at the start. The cost of that extra capacity should be weighed against the lower tier rebate. See the tier breakdown.
The factor also falls every six months, 6.8 at the time of writing and 5.7 from 1 January 2027, so the value of the one claim you get shrinks the longer you wait. The battery STC calculator will show the difference.
What this means for installers
Ask at quote stage whether any battery has previously been installed at the premises and whether it received a discount. Record the answer in the job notes. A claim for a second battery on the same address is likely to be rejected, and the customer will have been quoted a price that assumed a discount that does not arrive. The installer checklist covers the rest of the pre-quote checks.
What this means for you
If you already have a battery, work out whether it ever received the discount. If it did not, you may still have a route for added capacity. The battery STCs pillar sets out the program rules, and /pricing/ shows how certificate value is passed through to installers.