Trying to work out the right battery size for your home can start to feel confusing. Choosing a battery that's too small will make it harder to achieve decent electricity bill savings, while one that's too large might leave you paying for more than what you need. 

Finding the right size comes down to five things – your energy use at night, your solar system (if you have one), your electricity tariff, whether you want backup power and your future energy needs. If you’d prefer an instant recommendation on a battery size to suit your home and energy needs, you can also complete our two-minute online form.

This guide explains how battery capacity works in simple terms, what you should consider when working out the right size for your home and how to make sense of common battery sizes. It should give you enough of a head start to have a confident chat with an installer, without needing to become a solar engineer first!

What does 'battery size' actually mean?

Battery size is measured in kilowatt-hours (kWh), which tells you how much energy the battery can store. You’ll often hear this referred to as it’s ‘capacity’. For example, a 10kWh battery can hold 10 kilowatt-hours of electricity, which would be enough to power a few big appliances at night.

However, you can’t use all the energy stored in a home battery. Most batteries keep a little energy in reserve to protect the system and support longevity. Even if a battery is labelled as 10 kWh, the amount you can rely on day-to-day is usually a bit less - often around 9 to 9.5 kWh. This is known as ‘usable capacity’ and it’s the number you should focus on when shopping for batteries.

It's also helpful to understand the difference between a battery's capacity and its power. Capacity (kWh) is how much energy the battery can store, while power (kW) tells you how quickly it can deliver that energy to your home. A battery with high capacity (kWh) but low power output (kW) may struggle to run many appliances at the same time, even if it has plenty of energy stored inside. Both numbers matter when finding the right battery size for your home.

The five key questions to help you work out your battery size

1. How much energy do you use at night?

This is the biggest question to think about. Your home battery should look to cover your energy needs at night, when your solar panels stop producing energy from the sun. Think about how much energy you use from the late afternoon through to the next morning. For many Australian homes, this sits somewhere between 8 and 16 kWh, but it varies widely.

Tip: Your electricity retailer might provide hourly breakdowns of your usage via your online account. You can also confirm your latest electricity bill amount in our two-minute online form and Zelora will recommend a suitable battery size for your home, based on your energy usage.

2. If you have solar panels, what is the size of your system?

A battery can only store the energy your solar panels produce, if this amount exceeds the energy you would use during the day. This is often called ‘surplus’ energy. If your solar system is small or your daytime energy usage is high, there may not be enough surplus energy to fully charge a large battery each day. Matching your battery size to surplus energy, not just solar panel capacity, is important. 

3. What is your electricity tariff structure?

Your electricity plan tariff often affects how much money a battery can save you. Some households pay different rates depending on the time of day, known as a ‘time-of-use tariff’. Their electricity costs more during peak times (typically 3-10pm); which is the same window that a battery would normally supply a home with energy.

If your battery size is large enough to cover most of your usage during peak hours, you’ll save more money than someone on a ‘flat rate’ tariff, who pays the same price for electricity all day, every day. This means your tariff type plays a big role in how much each stored kilowatt-hour (kWh) of energy is worth to you.

4. Do you want backup power?

If having power during a blackout is important to you, look at sizing up your battery beyond your everyday needs to give you a buffer. Keep in mind that not all batteries support a backup operation - it depends on the brand you choose. Make sure you double-check any quotes to confirm if this is included. Zelora offers battery systems with backup protection that can be configured to suit your needs.

5. Are your household energy needs likely to change in future?

If you're thinking about an electric vehicle (EV), looking to switch some items from gas to electric or if your household is growing, your energy needs will increase. It’s often more cost-efficient to get a larger battery now, versus trying to increase battery capacity down the track. Our two-minute online form can also factor in your future energy needs to help work out the right battery size for you. 

Common solar battery sizes and what they suit

To help you make sense of battery sizes, the below table offers a general guide on common sizes and what they’re best suited for. Keep in mind that these ranges are indicative only. Your ideal battery size should be determined by looking at electricity usage data, your solar system size and your own priorities.

*Actual duration depends on usage and solar recharge availability.

How long does a home battery typically last?

When it comes to a battery’s lifespan, most will come with warranties or a guaranteed number of usage cycles, which is simply the number of times that 100% of the battery’s stored energy is used. Over time, all batteries will gradually decline in their charge capacity, meaning a 10 kWh battery might retain around 70 to 80% of its original capacity by the end of the warranty period. This is normal and expected, just like how a mobile phone battery degrades with age.

Using the warranty period as a reasonable guide for how long the battery might last is a useful approach when thinking about the long-term value for you and your home. If you’re keen to take a closer look at the financial side, our costs and savings articles can help you learn more.

When might a larger battery not make sense?

It’s tempting to think that bigger is better when it comes to batteries, but that’s not necessarily the case. A larger battery will cost you more, and if your solar system doesn’t produce enough surplus energy to charge it fully most days, you might be paying for capacity that you don’t use.

The right approach is to match the battery to your actual usage and solar surplus, not to default to the largest option available. If you’re not sure where to start, Zelora can recommend a size to suit your home and energy needs via the two-minute online form.

Frequently Asked Questions

What size battery do I need for an average home?

For a typical Australian household with basic energy needs, an 8-16 kWh battery is a decent starting point. The right battery size depends on your actual energy consumption patterns, solar system output, and whether you want backup capability in a blackout. It’s important to remember that there is no single answer to this question. Your home energy data is the best guide to help determine the right battery size. 

Is a bigger battery always better?

Not necessarily. Buying a battery that’s larger than your solar surplus can fill or that your overnight usage will drain, means you’re simply paying for unused capacity. The goal should be to match the battery size to your realistic energy needs, not to oversize the battery for scenarios that rarely occur.

Can I use a home battery calculator to choose the right size?

Online solar battery size calculators can give you a rough starting point on suitable battery sizing, but they typically can’t account for all the different variables that should be considered. Your tariff structure, seasonal energy usage shifts, roof shading and future changes to your energy needs should all be considered when determining the right battery size for you. In summary, online solar battery calculators are a useful first step, but they should not be used as a substitute for proper assessment from a qualified installer like those in the Zelora team.

Do I need a battery if I already have solar? 

If you’re happy with your current savings and your feed-in tariff provides reasonable value for any surplus exports, solar may continue to work well for you. However, a new battery can add value when there’s a gap between your feed-in rate and your electricity purchase rate, and when you use a lot of energy at night.

Is there a way to get a battery without paying upfront?

Yes. Some brands like Zelora offer subscription plans where you pay off your system via a simple monthly fee, instead of buying your system upfront. This can make buying a battery more accessible. Zelora offers subscription and outright purchase options, so you can choose what’s right for you. Our pricing page covers how these plans work and what to consider.

Final thoughts

The most reliable way to determine what size battery you need is to look at your energy data. Grab your latest electricity bill, check your average daily usage and see how much of that usage falls in the evening and overnight. You should also think about whether your energy needs are likely to change in the future, as that could mean you need to size up slightly.

You can always get a battery size recommendation from Zelora by using our two-minute online form. If the big upfront cost is a concern, our pricing page outlines subscription plan options with simple monthly payments and additional benefits like optimisation.

The right battery size is the one that matches your home’s real energy needs. It’s not about buying the biggest one you can afford or the cheapest one available. Take the time to get it right, and you’ll enjoy the benefits of investing in a battery for many years to come.