Can you add a battery to plug-in solar in WA?

The battery section is one of the places where WA’s draft goes beyond the German standard it is based on. The consultation paper calls it an “extra section to allow plug-in battery storage”, with type tests taken from existing battery standards. The government expects most plug-in batteries to be 5 kWh or less. The FAQ says a battery of about that size is enough to run a fridge, router and standby appliances overnight. None of this is legal yet: it is a draft out for comment until 5pm AWST on 9 December 2026.

How would a plug-in battery connect?

On the DC side of an inverter, and in a kit with panels, the same inverter as the solar panels. The draft says a battery only forms part of the same plug-in generator if it is “connected to the DC side of the same inverter as the solar modules” (section 1). It must use a DC input the inverter maker has designated for a battery, and must not be connected to the house wiring or the grid any other way (section 6.5).

This matters because of the one-per-household rule. A solar kit with its own inverter and a battery with its own inverter count as two plug-in generators, and the draft allows only one per household. So in practice the battery and panels have to share one inverter.

The draft also lists a battery-only system as a device type (section 4.2.2). It may charge from the grid through the ordinary plug, but its draw must not exceed 800 VA (section 6.5.1).

Is there a size limit?

No capacity limit is proposed. Two power limits still apply to the whole kit, battery included:

• The inverter can push no more than 800 VA and 3.5 A into your home (section 4.1).
• The combined PV and battery output on the DC side must not exceed 2,000 W (section 4.1). Where the panels and battery use separate DC inputs, the maker must show this limit holds “under all normal and single-fault conditions” (section 6.5.3).

My arithmetic: at a steady 800 W, a 5 kWh battery would take about six and a quarter hours to empty, so it suits a slow, steady evening load more than a kettle or oven.

Which battery chemistries are allowed?

Only lithium iron phosphate (LFP) and sodium-ion (Na-ion). The draft says batteries using lithium nickel-manganese-cobalt (NMC) chemistry “are not permitted” (section 5.8). Other rules on the cells (section 6.5.1):

• Only new cells. Second-life, reconditioned or repurposed cells are banned.
• The battery must be rated for ambient temperatures of at least 55°C. The draft does not say why, but my reading is that a hot west-facing Perth balcony in summer is the kind of place it has in mind.
• The maker must declare the chemistry, nominal voltage, usable capacity, cell format and part numbers.
• The battery must come as part of a complete kit tested and declared compatible with the specific inverter. The draft says compatibility “must not be assumed” between a battery and inverter that have not been jointly certified.

What does the battery management system have to do?

Cut the battery off by itself when something goes wrong. The battery management system (BMS) monitors charge, discharge and temperature. On any out-of-limit condition, the draft says it must “independently disconnect or isolate the battery from the inverter, without reliance on any action by the inverter, the inverter’s AC-side protection, or the user” (section 6.5.2).

It must also be fail-safe. Loss of communication with the inverter, loss of power to the BMS, or a fault inside the BMS must each leave the battery disconnected. Any BMS software must meet annex B of AS/NZS 62109.1:2026.

What other wiring rules apply on the DC side?

Section 6.5.3 sets these:

• A battery must not share a DC input with a panel string unless the maker has evaluated and declared that setup safe.
• The battery’s voltage across its full charge range must stay inside the inverter’s DC input range.
• No reverse or fault current may flow from the battery into the panel circuit, or from the panels into the battery outside the BMS’s normal charge control.
• If a battery plug could be pushed into a panel socket, the connectors must be keyed or of a different type so that cannot happen.

What about fire and venting?

The enclosure and the way cells are packed must limit thermal runaway spreading from one cell to the next. Enclosure materials must be rated at least UL 94 V-0 for flammability, or shown by test to be as good. If the battery can vent gas in a fault, the gas must be directed away from occupied rooms, ignition sources and escape routes, and a battery meant for indoor mounting “must not vent directly into the interior of the dwelling” (section 6.5.2).

What labels and paperwork come with a plug-in battery?

Section 6.5.4 requires:

• markings in line with IEC 63056:2020
• a Safety Data Sheet, also reachable by a QR code fixed or embossed on the top of the unit
• a green reflective label at least 100 mm across, printed “ES - Plug in” with the United Nations number for the battery chemistry, which you stick on your switchboard

The solar kit itself comes with a separate green “PV - Plug in” switchboard label (section 8.2.3). My reading is that both labels are there so an electrician or firefighter can see at the switchboard that a plug-in generator and a battery are in the home.

The maker must also declare how many cycles and years the battery should hold its usable capacity, and under what conditions (section 6.5.2).

Which type tests must a plug-in battery pass?

On top of the general kit tests in section 9.2, section 6.5.6 adds:

Topic	Test	Pass criteria
Cell and battery stress	IEC 63056:2020	Compliant summary covering every listed category
Thermal propagation	AS IEC 62619:2023, on the complete battery as supplied	No spread of thermal runaway beyond the first cell, or hazard contained
Enclosure fire performance	UL 94 flammability	Not lower than V-0
Transport	UN 38.3	Compliant T1 to T8 summary
BMS software	Annex B of AS/NZS 62109.1:2026	Compliant
DC voltage compatibility	Circuit analysis across full charge range and PV range	Stays within the section 4 limits

The IEC 63056 testing must cover, as a minimum, cell tests for external short circuit, impact, drop, thermal abuse, overcharge, forced discharge, internal short circuit and propagation, plus system tests for edge and corner drop, overvoltage, overcurrent and overheating protection (section 6.5.2). Grid-chargeable systems also have their AC charging draw measured at 207 V, 254 V and nominal voltage, and must not exceed 800 VA (section 9.2).

Is this the same as a home battery?

No. The draft says section 6.5 “does not apply to hard-wired battery energy storage systems (e.g. home batteries)”, which stay under the full AS/NZS 5139:2019 rules. A plug-in battery is a small appliance-style unit. A home battery is installed by an electrician into your switchboard. Consultation questions 9 and 12c ask whether the battery controls are adequate and what is missing.

Would a plug-in battery get the WA or federal battery rebate?

It looks unlikely under either scheme as written. Neither scheme page mentions plug-in batteries by name, so this is my reading of their stated rules.

WA Residential Battery Scheme. The eligibility page (updated 15 April 2026) requires at least 5.0 kWh of usable capacity, products on the Clean Energy Council’s approved battery and inverter lists and on the Synergy or Horizon Power Supported Solution List, an installer who is a licensed electrician holding a Grid Connected Battery Systems accreditation with Solar Accreditation Australia, and joining a virtual power plant. Synergy customers get $130 per kWh up to $1,300. Horizon Power customers get $380 per kWh up to $3,800. Under the draft, plug-in kits would not go through Clean Energy Council approval and you install them yourself, so a plug-in battery would miss at least the listing and installer requirements.

Federal Cheaper Home Batteries Program. The DCCEEW eligibility page (updated 1 May 2026) says: “Portable batteries and electric vehicles are not eligible under the program.” It also requires 5 to 100 kWh nominal capacity, CEC listing, installation by or under on-site supervision of an SAA-accredited battery installer, and a battery installed with solar PV. Retailers must give assurance the battery “will be installed for permanent use and would not be moved or on-sold”. A plug-in battery is built to be moved, so it appears to fall outside the program.

Is a battery worth it?

It depends on what it costs and when you use power. The government’s estimate gives about $260 a year extra from adding a battery. At Synergy’s A1 rate of 33.2621 cents per kWh, that is about 780 kWh a year of solar moved from midday to the evening. Example payback sums are on cost and savings, and the safety side is on plug-in solar safety.