What size batteries do UK households install?
DESNZ publishes official statistics on home batteries registered with MCS. They are about cost as well as size, but this guide uses only the size side: what households chose, and how that changed in a year.
In short
In 2025/26 the average battery registered with MCS in an existing home was about 9.6 kWh nominal (DESNZ, our arithmetic). 37.9% were under 6 kWh, 33.7% were 6 to 11 kWh and 28.4% were 11 kWh or more, the biggest band having grown from about a fifth of the sample the year before.
The 2025/26 figures by size band
| Size band (nominal) | Batteries | Share | Total capacity | Average size |
|---|---|---|---|---|
| under 6 kWh | 16,270 | 37.9% | 83,560 kWh | 5.1 kWh |
| 6 to 11 kWh | 14,457 | 33.7% | 141,650 kWh | 9.8 kWh |
| 11 kWh and over | 12,176 | 28.4% | 188,540 kWh | 15.5 kWh |
Across the whole sample of 42,903 batteries, total capacity divided by the number of batteries gives an average of about 9.6 kWh nominal. The year before, the same sum gave about 8.7 kWh across 23,896 batteries.
How the mix moved in a year
Between 2024/25 and 2025/26 every band grew, but not equally. Batteries of 11 kWh and over went from 4,926 to 12,176 in the sample, more than doubling, and their share rose from about 20.6% to 28.4%. The small band's share fell from about 43.9% to 37.9%. The average size within each band also edged up.
DESNZ's monthly sheet counts 24,242 batteries recorded in existing homes in 2024/25 and 44,033 in 2025/26. DESNZ notes that a rise in registrations may reflect more batteries being fitted, more being registered with MCS, or both.
What the figures cover, and what they don't
- Only batteries registered with MCS, in homes that already existed. New builds, commercial installations and batteries never registered with MCS are outside them.
- Nominal capacity, as recorded by MCS. Usable capacity is usually a little lower, and that is what matters for sizing.
- Batteries under 1 kWh or over 30 kWh were removed by DESNZ before calculating, along with extreme cost entries.
- They are official statistics in development, and DESNZ revised some earlier months in the May 2026 release as more records arrived.
Using these figures sensibly
The statistics say what other households chose, not what suits yours. A home with a small evening load and modest panels may be well served by the smallest band; a home with a heat pump, an electric car or a large array might sensibly sit in the biggest. The trend towards larger batteries says something about the market, but a bigger battery that seldom fills or empties is energy storage you are not using.
Two checks keep the numbers honest for your own decision. First, size from your own use after dark, as what size battery does. Second, look at how the seasons affect your surplus, as the seasons guide shows. If a quote proposes a size far from both, ask why.
And if a quote quotes a single "size", ask whether it is nominal or usable, and get both in writing. Comparing specifications explains the rest of the datasheet.
Why the average is creeping up
DESNZ doesn't say why households are choosing bigger batteries, and we won't guess at reasons it hasn't given. What the figures do show is that each band's average grew a little as well as the large band's share: the mid band's average rose from about 9.4 to 9.8 kWh and the large band's from about 15.0 to 15.5 kWh between the two years (our arithmetic from DESNZ's totals). Whatever the cause, a rising average is a reminder to size from your own evenings rather than from what is common.
Limits on very large systems
Bigger is bounded. PAS 63100 caps a single enclosure at 20 kWh and most homes at 40 kWh, or 80 kWh where the batteries are outdoors, in a detached garage or outbuilding, or in a suitably separated garage. DESNZ's statistics also leave out anything over 30 kWh. Where a battery can go explains the caps.
Nominal sizes in quotes
Because the statistics count nominal capacity, a quote that uses the label size is directly comparable with them, but not with your evening use. Before setting a quoted size against these figures or against your own needs, check which one the quote gives. Comparing specifications shows where both appear on a datasheet.
How to read your own place in the figures
Work out your usable size from your own evening use with the sizing helper, then add back the small margin most batteries hold in reserve to get a rough nominal size. Find the band it falls in. If you land in the small band, you are in the company of more than a third of recent installations; if you land in the large band, a little over a quarter. Neither is a reason to change your answer. The figures tell you what is common, and the helper tells you what fits.
When DESNZ publishes its next annual figures, usually in late May, we will update this page with a third year.
What this page is based on
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