At a glance
Battery capacity should be matched to the energy you can realistically charge and use. Bigger is not automatically better: usable capacity, charge and discharge power, efficiency, operating reserve and warranty all matter.
What to have ready
- Half-hourly or daily electricity consumption data
- Existing or proposed solar-array output
- Import, export and time-of-use tariff rates
- Essential loads you may want to support
- Future demand from an EV or heat pump
Capacity and power are different
Capacity, measured in kilowatt hours, describes how much energy the battery can store. Power, measured in kilowatts, describes how quickly it can charge or supply the home. A battery may hold enough energy for the evening but still have a power limit below the demand of several large appliances running together.
Use real consumption patterns
For solar charging, compare daytime surplus with evening and overnight demand. For tariff charging, examine how much energy can be imported during the cheap window and how much peak-rate consumption it can replace.
A design based only on annual consumption can miss these timing constraints.
Clarify what backup means
Not every battery provides power during an outage. Systems that do may support only nominated circuits and can have different power limits in backup mode. Decide whether backup is important and which loads are genuinely essential before comparing proposals.
Compare the whole proposal
Ask about usable rather than headline capacity, round-trip efficiency, expected degradation, warranty throughput, installation location, fire-safety requirements, monitoring and compatibility with existing solar equipment.
Common questions
Independent sources
Guidance can change. Check the latest information before making a decision.
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