What size home battery do you need?

Energy (kWh) and power (kW)

A home battery has two sizes. Capacity in kilowatt-hours (kWh) is how much energy it stores. Power in kilowatts (kW) is how much it can deliver at once. A 13.5 kWh battery with 5 kW of continuous power can run a 5 kW load for under three hours, or a 1 kW load for more than half a day, but not an 8 kW load at all. Homes with heat pumps, electric cooking or EV charging often find power, not capacity, is the limit; many systems add power by stacking battery modules or adding inverters.

Sizing for solar self-use

Most batteries are bought to store daytime solar power for the evening and night. Your bills or smart meter data show how much electricity the home uses each day; the battery needs to cover the part used when the panels produce little.

1. Find your average daily use, for example 20 kWh.
2. Estimate the share used from late afternoon to morning; in many homes it is half or more, say 11 kWh.
3. Check that your solar array produces enough surplus on a typical day to fill that much storage after covering the daytime load.
4. Choose a usable capacity close to that overnight figure, here 10 – 13 kWh. A larger battery only pays if the panels can fill it most days.

Where tariffs vary by time of day, a battery can also charge from cheap off-peak power and discharge in the evening peak, and in a virtual power plant it can earn payments for supplying the grid at times of high demand.

Sizing for backup

For outages, decide which circuits must run: typically the fridge, lighting, internet, a few sockets and perhaps a well pump or gas boiler controls. Add up their power to choose the kW rating, and multiply by the hours of outage you want to ride through for the kWh. Check that the system offers backup at all: some batteries only work while the grid is up, and backup usually needs a transfer switch or gateway installed with the battery. Whole-home backup with air conditioning or electric heating needs high power and often two or more battery units.

Usable versus nominal capacity

Nominal capacity is the energy the cells hold; usable capacity is what the system lets you draw, after the reserve that protects the cells. Brands quote one or the other, so compare like with like. Australia's Clean Energy Council approved list states both for every model: across 1,786 models the median usable share is 98%, but individual products range lower. Australian incentives are calculated on usable capacity.

What sizes are on the market

Nominal capacity of the 1,786 battery models on Australia's approved list, most of them configurations of modular systems:

Modular systems let you start at 5 – 10 kWh and add modules later, but adding modules years later can be limited by product availability and warranty terms; ask the installer before relying on it.

Incentives in 2026

Australia: Cheaper Home Batteries Program

The federal program discounts a battery through small-scale technology certificates (STCs) created for each kWh of usable capacity. The Clean Energy Regulator sets the factor per kWh, and it steps down over time: 8.4 from January to April 2026, 6.8 from May to December 2026, 5.7 in the first half of 2027 and 5.2 in the second half. Since May 2026 the first 14 kWh receive the full factor, capacity from 14 to 28 kWh 60% of it and from 28 to 50 kWh 15%; no certificates are created beyond 50 kWh of usable capacity.

To qualify, the battery must be on the Clean Energy Council approved list, between 5 and 100 kWh nominal, installed by a Solar Accreditation Australia accredited installer to AS/NZS 5139:2019, paired with a solar system, and capable of joining a virtual power plant. The approved status of each model is shown on its PowerTrusted product page.

United States: the federal credit has ended

The 30% Residential Clean Energy Credit (section 25D), which covered home batteries, was terminated by the 2025 budget law for systems placed in service after 31 December 2025. State and utility programmes continue in some places, so check your state energy office and utility before buying. For grid-connected systems, US building and fire codes call for batteries listed to UL 9540.

Before you sign

• Usable capacity and continuous power in kW, in writing.
• Whether backup is included, which circuits it covers and the switch-over time.
• Warranty in years and in energy throughput or cycles, and the capacity guaranteed at the end.
• Certification: the Clean Energy Council approved list in Australia, UL 9540 in the US, VDE-AR-N 4105 in Germany.
• Compatibility with your existing solar inverter, or whether a hybrid inverter is needed.

Compare 784 home battery ranges by capacity, power, brand and market.