How to Choose a Home Battery in NZ

Before comparing brands and kWh figures, there are bigger questions to answer first. Here's the decision process that should come before any battery purchase.

Work out if you need solar first

A home battery without solar panels can still be useful — mainly for load shifting, charging on cheap off-peak power and using it during expensive peak periods, and as backup during outages. But the biggest financial case for a battery comes from storing your own solar generation rather than exporting it cheaply back to the grid. If you don't have solar yet, it's worth getting a solar quote alongside any battery quote, since installing both together is usually more cost-effective than adding a battery later.

Understand what problem you're actually solving

Before sizing anything, get clear on your main goal. Is it reducing your power bill, having backup power during outages, maximising use of solar you already generate, or some combination? Each goal points toward a different sized system, and installers will size a battery very differently depending on which one matters most to you.

Size the battery to your actual usage, not a generic figure

Pull up your last 12 months of power bills and look at your average daily usage in kWh — most NZ retailers show this in their app or portal. A household using around 15-20kWh a day has very different battery needs to one using 8-10kWh. Rather than accepting a generic "family-sized" recommendation, ask your installer to size the system against your specific usage pattern and your solar generation, if you have it.

Ask what happens during a power outage

Not all battery systems provide backup power during a grid outage — some are designed purely for cost savings and won't function at all when the grid goes down unless specifically configured for it. If outage backup matters to you, particularly if you're in an area prone to weather events, ask directly whether the quoted system includes this and which circuits in your house it would actually keep powered.

Ask about warranty and expected lifespan

Home batteries are typically warrantied for somewhere between 10 years and a set number of charge cycles, whichever comes first. Ask installers to explain both figures in plain terms, and what capacity the battery is guaranteed to retain by the end of the warranty period — most degrade gradually, and a battery only guaranteed to retain 70% capacity after a decade behaves differently to one guaranteed at 80%.

Ask how it integrates with your power plan

Some batteries work best paired with a specific time-of-use electricity plan that has cheap off-peak and expensive peak rates, letting the battery charge cheap and discharge expensive. Ask your installer whether your current power plan suits the system being quoted, or whether switching retailers or plans would meaningfully improve the payback period.

Get more than one quote

Battery and solar installer quotes in NZ vary significantly for broadly similar hardware. Get at least two or three quotes, and ask each installer to show their sizing assumptions and expected payback period in writing, not just a total price — this makes it much easier to compare quotes on equal terms rather than just comparing sticker price.

Ask about future expansion

If budget is tight now, ask whether the system can be expanded later — some battery platforms allow adding a second unit down the track, while others require replacing the whole system to increase capacity. This matters if you expect your household's power usage to grow, for example if an EV purchase is on the horizon.