What size battery do I need?
Jason Hawthorne, CEO at ESME
Rates checked October 2026 · 5 min read · Last updated 22 October 2026
In short
Size a battery to the electricity you use outside your cheap hours, not to the biggest one you are offered. For most homes that means about 5kWh for a smaller home and 10kWh for a larger one. Check the usable capacity and how fast it can power the house, as well as the headline size.
For your house
What size suits your house?
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Key facts
Typical small home
1,600 units a year, about 4.4 a day
Typical medium home
2,500 units a year, about 6.8 a day
Typical large home
3,800 units a year, about 10.4 a day
Sensible starting sizes
About 5kWh for smaller homes, 10kWh for larger ones
Cost per usable unit
About £400 to £700 per kWh, installed
Where do I start?
Start with your bills or your smart meter app. Find how many units you use a year, then how much of that falls outside the cheap hours of your tariff. That second number is what the battery needs to cover.
1 to 2 people, flat or 1 bed
Units a year
1,600
Units a day
4.4
Starting size
About 5kWh
2 to 3 people, 2 to 3 beds
Units a year
2,500
Units a day
6.8
Starting size
5 to 10kWh
4 to 5 people, 4 or more beds
Units a year
3,800
Units a day
10.4
Starting size
10kWh or more
Ofgem typical consumption values from July 2026. Your own use may be very different, so use your real figures.
What do usable capacity and power mean?
- Usable capacity is how much the battery can actually give you. Some batteries keep part of their charge in reserve, so it can be less than the number on the box.
- Power, in kW, is how much it can supply at once. A Tesla Powerwall 3 gives up to 11.5kW and a GivEnergy All in One 6kW. If the kettle, oven and shower all run at once, a low power battery leaves the grid to cover the rest.
- Charge time matters too. The battery has to fill inside your cheap hours, which may only be three to six hours long.
What does an electric car change?
An electric car usually charges straight from the grid in the cheap hours, so you do not need a battery big enough to charge the car. What the car does is move you onto an electric car tariff, with cheaper and often longer cheap hours. That makes a bigger battery worth more, because every unit it shifts saves more.
If a car is likely in the next few years, size the battery and tariff for that home, not today’s.
Is bigger better?
Only if you use it. Every kWh of capacity costs about £400 to £700, and a battery that is never emptied earns nothing for the extra. With solar, a bigger battery can store more summer sunshine, but in winter it will mostly fill from the grid. See will a battery pay back.
Questions people also ask
Is a 5kWh battery enough?
For a smaller home, often yes. If most of your use is in the evening and you use around 5 units outside the cheap hours, a 5kWh battery covers most of it.
Can I add more capacity later?
Some batteries can be extended with extra modules. Check before you buy, because others cannot be added to.
Should I size the battery to my solar panels?
Size it to your use first. Solar helps fill it, but in winter most of the charge comes from the grid.
Sources
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Figures are for Great Britain and were checked on the date above. Prices change, so check the latest before you decide. This is general information, not financial advice.
Your house, not an average one
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