Money · Cost note
An 8 kWh home battery
Updated
Around 8 kWh is a common middle: enough for many evenings, possible to fill from a decent summer array, and not so large that winter grid-charging becomes the whole point. Check usable capacity rather than the badge.
The figure, and what it leaves out
The opening is the claim. What follows is how I would test it against a bill, a cupboard and a connection form. People still want a number. A fair illustration for this 5 kWh example is £3,650 fitted at the temporary 0% residential rate, before a new board, scaffold, a long cable or a gateway.
Take a 5 kWh pack, cycled about 260 times, at 90% round trip. Charge at 7.0p, and value what comes back at 26.0p. Export given up is priced at 4.0p. There are no panels beside this 5 kWh pack, so every unit charged comes off the grid. Delivered energy is about 1170 kWh. After charging cost and lost export, the figure saves about £213 a year. Set that against £3,650 fitted, which is a September 2026 illustration at the temporary 0% residential rate, not a quote. That is a simple payback of about 17.1 years, which is past a typical 10-year warranty. Nudge the night rate up by 4p and see if you still like it.
Lines that move the total
In most single-phase houses in Britain, 3.6 kW is in the band where G98 connect-and-notify is often enough. Export can still be capped. Agree that before the inverter is ordered. The figure uses 5 kWh and 0 kWp, which is enough to tell two quotes apart if they assumed something else.
A consumer unit with no spare way is extra. A gateway is extra, and only if backup was the brief. Exclusions are fine when they are written down. Hidden ones are why two quotes sit thousands apart.
A number I would not chase
Where the job is a qualifying install in a home, the 0% rate runs to 31 March 2027 and is due to become 5% after that. This figure prices the work at £3,650 on that basis. It does not apply to a shop, and it does not apply to a battery you buy and fit yourself.
I would not sign off a 5 kWh install from a video call. Someone has to open the consumer unit. Price per kWh is a blunt tool. Put inverter kilowatts and the name that honours the warranty back into the comparison.
Before a deposit, I would want usable capacity, the warranty counterparty and a G98 note for this 3.6 kW inverter. The cupboard has to be a place you can stand in, at a temperature the datasheet allows. A five-minute video is not that.
Common questions
Is the price on this page a quote?
No. £3,650 is a September 2026 illustration for a 5 kWh example at the temporary 0% residential rate. Your survey replaces it.
Will it stay on in a power cut?
Only if a gateway or essential-load board was designed and paid for. A standard grid-tied battery turns off with the grid. On this 5 kWh example the inverter is 3.6 kW, and backup is still a separate line.
What paperwork should I keep?
Keep the MCS certificate where the job is certified, the electrical certificate, the DNO record, the schematic, the warranty registration and a photo of the schedule. For an illustrated £3,650 job, that folder is part of what you bought.
What if the cheap rate is not 7p?
Then the figure changes. This page used 7.0p as a charge rate and 26.0p as the rate avoided. A smaller gap means a worse payback. Read the live tariff.
Sources
Want a price for your house?
The figures above are a rough guide. An installer still needs to see your fuse board, where the battery will go, and whether you want power during a blackout.