The short answer
10 kWh battery, retrofit
£4,500–£6,500
Added during a solar install
£4,000–£6,000
Typical annual saving
£450–£700
All prices installed, including 0% VAT. "10kW" almost always means 10 kWh of storage — the industry's sloppiest habit, decoded below.
Why our prices look lower than other sites
Some comparison sites quote £8,000–£10,000 for a 10 kWh battery. Those are brand list prices — not what installers actually charge. Our figures come from real UK installer quotes collected monthly. They include 0% VAT, standard installation labour, and the inverter where it is bundled. We would rather give you the real number and have you pleasantly surprised than the other way round.
Why 10 kWh is the UK's most popular size
For a typical 3–4 bedroom home with 4–5 kWp of solar, 10 kWh of storage catches most of the spare generation without wasting money on capacity you will rarely fill. A 5 kWh battery leaves export on the table from March to October. A 13.5 kWh battery costs £2,000 more and rarely cycles fully — dead money on the wall. Use the battery size finder to check what capacity your home actually needs.
What pushes the price up or down
| Factor | Effect on price | Notes |
|---|---|---|
| Retrofit vs new install | +£500–£1,000 for retrofit | Extra labour, separate inverter |
| Location | ±£300–£500 | London and South East labour rates are higher |
| Inverter choice | £800–£1,500 if not included | Check if your quote bundles the inverter |
| Scaffolding | £400–£700 | Almost always needed for the solar side |
| Brand | £1,500 spread | Fox ESS vs Tesla — same kWh, different badge premium |
| EPS / backup wiring | +£300–£600 | Separate circuit for power-cut protection |
| Battery location | ±£200 | Loft installs cost more, garage is cheapest |
| 0% VAT | Saves £750–£1,100 | Universal since Feb 2024 — check your quote |
10 kWh battery vs bigger sizes
The cost per kWh drops with size, but only if you actually cycle the extra capacity. Here is how the sizes compare.
| Capacity | Installed price | Cost per kWh | Best for |
|---|---|---|---|
| 5 kWh | £2,500–£4,000 | £500–£800/kWh | Flats, 1–2 bed homes |
| 10 kWh | £4,500–£6,500 | £450–£650/kWh | Sweet spot for most homes |
| 13.5 kWh | £6,500–£8,500 | £481–£630/kWh | High evening use or an EV |
| 16+ kWh | £8,000–£10,500 | £500–£656/kWh | Large homes, heat pumps, full backup |
The cost per kWh drops with size, but only if you actually cycle the extra capacity. A 13.5 kWh battery in a home that only uses 6 kWh overnight is £3,000 of battery that sits there doing nothing most days. Size from your usage, not the spec sheet.
When does a 10 kWh battery pay for itself?
At £450–£700 saved per year against a £5,000–£6,000 installed cost, a 10 kWh battery pays back in about 7–10 years — faster with solar (5–8 years), slower without (8–12 years). These are real numbers at July 2026 unit rates. If the price cap rises, payback shortens. If cheap overnight tariffs disappear, the grid-only case weakens.
Payback also depends on how fully you cycle the battery. A household that uses the full 10 kWh every evening saves more than one that only skims the top 4 kWh. The battery size finder shows the payback for your actual usage pattern.
Frequently asked questions
Almost never. The industry uses "10kW battery" to mean 10 kilowatt-hours (kWh) of energy storage — how much it holds. Power output (how fast it discharges) is a separate number, typically 3–5 kW for a 10 kWh battery. It is sloppy but universal. We use kWh throughout this guide.
Yes. Since February 2024, battery storage qualifies for 0% VAT whether or not it is installed with solar panels. This includes retrofits. If your installer is charging VAT on a battery install, they have got it wrong.
Almost never for a wall-mounted battery on an existing house. Ground-mounted systems may need it if they exceed 2.5m in height or sit forward of the principal elevation. Listed buildings and conservation areas have extra rules.
DC-coupled charges directly from your solar panels — more efficient (97–99%) but usually needs to be installed at the same time. AC-coupled has its own inverter and can be added to any existing solar system — slightly less efficient (93–96%) but far more flexible for retrofits.
Right size first. Quotes second.
Usage in, recommended capacity out. Then, if you want them, up to three quotes from vetted installers.