The regulator’s rule is that only one battery system is eligible for STCs per premises. A granny flat raises the question of what counts as a premises. The answer comes from how the buildings are connected to the grid, not from what they are called.
When a granny flat is part of the main premises
Most granny flats are fed from the main house switchboard and share its National Meter Identifier (NMI), the number that identifies a connection point. Where that is so, the electricity supply is one premises. A battery already installed and claimed for the house means a second battery for the flat would not be eligible for STCs.
When it might be separate
A secondary dwelling with its own NMI, its own meter and its own supply, particularly where it is a separate lot or a separately rented unit, looks more like its own premises. In that case a battery for that dwelling could stand on its own. We would not assume it, so before the quote:
- Check the NMI on each meter or bill.
- Check the address on council records and the electricity bills.
- Ask the regulator or your trader to confirm how the claim will be treated.
Which battery should claim
If the two buildings share one connection, claim once, and size one battery for the combined load. The first 14 kWh is counted at the full factor, so a single well-sized battery gives the best discount. The battery size limits page explains the tiers.
If the answer comes back that the granny flat is a separate premises, treat it as a second, fully independent job: its own battery, its own product listing check, its own photos and its own assignment form. Do not bundle the two into one claim.
What this means for installers
Record the NMI and the address on the job and ask whether a battery has already been claimed there. Duplicate claims for one premises are the kind of issue that holds up a settlement. Our battery submission guide lists the evidence to capture, and the claim must still pass the standard product and installer tests in battery product eligibility.
What this means for homeowners
If you have a granny flat, the safest planning assumption is one discount for the property. If the flat is separately metered and you are weighing a second system, ask for written confirmation before paying a deposit. Work out a single battery’s discount with the battery STC calculator.
Owners with several properties should read claiming on multiple properties. For the overview, see battery STCs; installers can see pricing and start trading.