For most UK homes, a battery of around 5 kWh covers a typical evening, and around 10 kWh suits larger families, homes with bigger solar systems, or anyone charging cheaply overnight on a time-of-use tariff. The right size for you depends on how much electricity you use after the sun goes down, how much spare solar you produce, and which tariff you are on. This guide walks through each of those in plain terms.
Start with how much electricity you use
The best starting point is your own usage. Your bill or energy app will show your annual kWh, and a smart meter can show you a daily pattern.
If you do not have your figures to hand, Ofgem’s typical domestic consumption value for electricity is 2,500 kWh a year, updated from 2,700 kWh in July 2026. That works out at roughly 7 kWh a day for an average home. Smaller flats may use much less, and homes with an electric car, heat pump or home office often use a lot more.
What matters most for a battery is not your total, but when you use it. A battery earns its keep by covering the hours when electricity is expensive and your solar panels (if you have them) are not producing. For most households that means early evening through to the next morning.
To estimate this, add up what your smart meter shows from around 4pm until the next morning on a typical weekday. That is roughly the most a battery could usefully cover each day.
Usable capacity versus total capacity
Battery sizes are quoted in kilowatt hours (kWh), but you cannot always use every one of them. Most batteries keep a reserve so they are not drained completely, which protects their life. The share you can actually draw on is sometimes called the depth of discharge.
The Energy Saving Trust gives the example of a system that stops discharging at around 20% of capacity. Many modern lithium batteries allow more than that, often around 90%. Some energy is also lost when charging and discharging.
So a battery sold as 10 kWh might give you roughly 8 to 9 kWh of real use each day. When you compare quotes, ask for the usable capacity, not just the headline figure.
If you have solar panels: match the battery to your surplus
With solar, the battery stores daytime electricity you would otherwise export, so you can use it in the evening instead of buying from the grid.
Two numbers set the useful size:
- Your evening and overnight use. There is little point storing more than you will use before the sun comes up again.
- Your typical daily surplus. On a bright summer day a 4 kW system can produce far more than a household uses, but on a grey December day it may produce very little. A battery only fills from solar on days when there is spare to store.
In practice, solar fills a battery well on perhaps two thirds of the days in a year and only partly in winter. Sizing for a sunny June day usually means a battery that sits half empty for much of the year. Sizing for your evening use, then checking it against your summer surplus, is a more balanced approach. Our solar and battery page covers how the two work together.
If you do not have solar: off-peak charging changes the maths
You do not need solar panels to benefit from a battery. With a time-of-use tariff, you can charge the battery overnight when electricity is cheap and run your home from it during the day and evening.
Some examples of tariffs people pair with batteries:
- Intelligent Octopus Go offers cheap whole-home electricity from 11:30pm to 5:30am, from around 7.6p per kWh, but you need a compatible electric car or charger.
- Octopus Flux is for homes with solar and a battery. Off-peak import from 2am to 5am has been around 15p to 17p per kWh depending on region, with higher export rates in the 4pm to 7pm peak.
- Cosy Octopus is for heat pump owners, with three cheap windows a day priced at roughly half the standard day rate.
For comparison, the Ofgem price cap unit rate from 1 October 2026 is 26.32p per kWh on average for direct debit customers. The gap between your off-peak rate and your normal rate is what a grid-charged battery saves you on every unit it shifts.
For battery-only homes, the size is mainly about your daytime and evening use. If you use 8 kWh outside the cheap window, a battery with around 8 to 9 kWh usable could, in principle, cover most of it. Tariffs and eligibility rules change regularly, so check the current terms before you decide.
A quick sizing guide by household
These are starting points, not quotes. Your own usage pattern matters more than the number of bedrooms.
| Household | Typical evening and overnight use | Suggested battery size |
|---|---|---|
| 1 to 2 people, flat or small house, out during the day | 3 to 5 kWh | Around 5 kWh |
| Average family home, around 2,500 to 3,500 kWh a year | 5 to 8 kWh | 5 to 10 kWh |
| Larger family, home working, or large solar system | 8 to 12 kWh | Around 10 kWh |
| Electric car, heat pump or very high usage, on an off-peak tariff | 12 kWh or more | 10 to 15 kWh, or more |
Most batteries can also be expanded later by adding modules, but not all. If you expect to buy an electric car or heat pump in the next few years, it is worth asking whether the system you choose can grow.
What a home battery costs in 2026
Prices vary with brand, size and the electrical work needed. Published UK figures suggest:
- Around 5 kWh: roughly £3,500 to £4,500 installed. Octopus, for example, has quoted from £3,947 for a 5 kWh battery-only install.
- Around 10 kWh: roughly £5,300 to £7,000 installed. Octopus has quoted from £5,336 for a 10 kWh battery.
Because the labour is broadly similar whatever the size, larger batteries usually cost less per kWh. That is why a 10 kWh battery often costs well under double the price of a 5 kWh one.
VAT is currently 0%. In Great Britain, home batteries have been zero-rated for VAT since 1 February 2024. This covers batteries fitted with new solar, batteries retrofitted to existing solar, and standalone batteries charged from the grid. The zero rate is due to end on 31 March 2027, after which it is due to return to 5%.
Is a battery worth it? An honest look at payback
The savings depend heavily on how you charge it.
Solar-only charging with a good export rate. If your tariff pays you, say, 15p for every unit you export, storing that unit and using it later only saves you the difference between 15p and your import rate of around 26p. That is about 11p per unit. As a rough example, a 5 kWh battery giving 4.5 kWh usable, filled on about 250 days a year, saves something like £120 a year. At around £3,500 installed, that is a very long payback, and potentially longer than the battery’s working life.
Off-peak charging. If you can charge at around 8p and avoid paying 26p, each unit shifted saves about 18p, and you can do it every day of the year. The same battery could then save roughly £290 a year, and a 10 kWh battery nearer £590. That brings payback down to around 10 to 12 years in these examples, before allowing for energy losses or changes in tariffs.
Combining solar in summer with off-peak charging in winter can improve things further. Our battery savings calculator lets you try your own numbers.
A battery can still make sense for other reasons, such as using more of your own solar, but it is best to go in with realistic expectations.
Lifespan, warranties and paperwork
Lifespan. The Energy Saving Trust puts the typical lifespan of a home battery at about 10 to 12 years. Manufacturer warranties are commonly 10 years, sometimes longer, and usually guarantee that the battery keeps a set share of its original capacity, often 60% to 80%. Some warranties also set a cycle limit, commonly around 6,000 full cycles. Check the retained capacity figure as well as the years.
Network operator. Your local electricity network operator needs to know about a battery that can export to the grid. Smaller systems, up to 3.68 kW per phase, usually come under the G98 process, where the installer notifies the network operator within 28 days of installation. Larger systems usually need G99 approval before installation, which can take several weeks. Your installer should handle this for you.
Frequently asked questions
Is a 5 kWh battery big enough?
For many smaller or average homes, yes. If your evening and overnight use is around 4 to 5 kWh, a 5 kWh battery will cover much of it. Larger families, high users and anyone charging overnight on a cheap tariff will often get more value from 10 kWh.
Can I add a battery to my existing solar panels?
Usually, yes. Batteries can be retrofitted to most existing solar systems, and a retrofitted battery currently qualifies for 0% VAT in Great Britain. The installer will check whether your current inverter is compatible or whether you need a battery with its own inverter.
Do I need solar panels to get a home battery?
No. A standalone battery can charge from the grid on a cheap overnight tariff and power your home at more expensive times. How much you save depends on the gap between your off-peak and standard rates.
Can a home battery power my house in a power cut?
Not automatically. Many systems shut down during a power cut for safety. Backup power needs specific equipment and wiring, so ask about it at the survey if it matters to you.
How long does a home battery last?
Around 10 to 12 years is typical, with warranties commonly running for 10 years. Capacity fades gradually over time rather than stopping suddenly.
The right battery is the one that matches when you actually use electricity, not the biggest one available. Solair Energy offers a free survey across Surrey, Sussex, Hampshire and London, looking at your usage, any existing solar panels and your tariff, followed by a fixed, written price. You can request a free quote or read more about home battery storage.