How to choose a home battery size
A battery's kWh number tells only part of the story. The useful starting point is how much energy you want to shift, when you need it and which loads matter.
On this page
Separate capacity from power · Match storage to your usage · Define what backup means to you · Compare modular and integrated options · Keep the decision grounded
Separate capacity from power
Capacity, usually shown in kWh, describes stored energy. Power, shown in kW, describes how quickly energy can be delivered. Compare usable capacity rather than assuming every advertised capacity figure uses the same definition.
Ask for both figures in your equipment schedule. Two batteries with similar stored energy can have different output limits and system configurations. The product datasheet helps identify those differences.
Match storage to your usage
Bring evening and overnight usage information, solar generation records if available, and your tariff details. Your Home explains how batteries can store energy for later use alongside rooftop solar.
As a discussion example, a household using 8 kWh after sunset should ask how usable capacity, backup reserve and system losses affect that requirement. The 8 kWh figure is a planning input, not an automatic battery recommendation.
Define what backup means to you
Write down the circuits or appliances you would want during an outage. Ask the designer to distinguish energy capacity, simultaneous power requirements and the proposed backup arrangement.
Do not assume a battery automatically backs up every circuit. Request a written description of included backup equipment, the supported loads, operating limitations and what happens when stored energy runs low.
Compare modular and integrated options
Some systems are configured using multiple battery modules; others combine storage and an inverter in a single platform. Ask which components are included in the quoted configuration and which can be added later.
Check manufacturer compatibility and expansion conditions before treating future capacity as guaranteed. A useful quote states the initial usable capacity and exact model codes, rather than only the product-family name.
Keep the decision grounded
Compare the installed scope, applicable warranty conditions, monitoring features and support arrangements. Ask for any savings estimate to identify its tariff, usage and operating assumptions.
Start with a realistic operating goal: shifting daytime energy, supporting selected loads during outages, or planning a broader electrification project. The best question is which configuration meets that goal at your property.
Your next step
Browse the battery guides and shortlist models, then ask for a capacity-and-power recommendation based on your usage.
Sources and further reading
Australian Government — battery technology ↗
General buying guidance. Equipment selection and installation requirements depend on your property and the proposed system.