A Surbiton household that already has an electric car often asks the same question when a home battery comes up: should the battery be big enough to charge the car? The short answer is no, and the reason is a matter of scale rather than technology. A car battery and a home battery do different jobs, and they are sized to different things. If the charger itself is the first step, our page on EV charger installation in Surbiton covers the job, from the semis towards Tolworth to the terraces around St Andrew’s Square.
Surbiton is a sensible place to ask. DVLA records 5,029 privately kept plug-in vehicles across Kingston upon Thames at the end of June 2026, up from 4,125 a year earlier, a rise of about 22% (our arithmetic). DESNZ records about 1,990 solar PV installations of all sizes across the borough at the end of 2025, as first published. More households are weighing up the car, the roof and the battery together.
Two batteries, two scales
The Energy Saving Trust says a typical home battery system might be 10 kWh, and puts a 5 kWh system at around £4,600. It also says there is no exact formula for sizing one: the answer comes from your own consumption.
A home charger works at a very different rate. A 7 kW charger puts roughly 7 kWh into a car for each hour it runs. On those two figures (our arithmetic):
- a 10 kWh home battery holds about an hour and a half of charging at 7 kW, even if it could deliver power that quickly;
- a 5 kWh battery holds well under an hour.
So a home battery large enough to fill a car would be sized to the car’s needs, not the house’s, and most of its capacity would sit unused on the days the car is away or already charged.
What the battery is for in a Surbiton house
A battery earns its place by moving electricity from when it is cheap or plentiful to when the house needs it, which for most homes is the evening. The seasons explain why that, rather than the car, sets the size. PVGIS estimates a 4 kWp south-facing array in Surbiton makes about 484 kWh in June, roughly 16.1 kWh a day, and about 137 kWh in December, roughly 4.4 kWh a day. December output is about 28% of June’s (our arithmetic). Set 4.4 kWh a day against a 10 kWh battery and a house that uses some of that output as it is made, and in winter a battery charged from the roof alone stays well short of full (our arithmetic), which is why it is often topped up from cheaper overnight electricity too.
The car, meanwhile, is usually charged most cheaply overnight, directly. Every new home chargepoint sold in Great Britain has had to be smart since 30 June 2022, so the charger can be scheduled into the off-peak window without passing the energy through the house battery first.
When the two do help each other
There are times the pairing is useful:
- Summer days with the car away. Surplus solar fills the house battery for the evening.
- Summer days with the car at home. With a compatible setup, surplus solar can go to the car instead.
- Winter nights. Off-peak grid electricity can top up both, the car through the charger and the house battery for the following evening.
What rarely helps is draining the house battery into the car in the evening, because the house then buys its own evening electricity from the grid. Our guide to adding a battery to existing solar in Surbiton covers the inverter choices if panels are already on the roof.
One supply, two devices
A 7.4 kW charger draws 32 A continuously, and most homes have a 60 A, 80 A or 100 A main fuse. A battery charging from the grid overnight adds its own load, so with both in the house, load management matters: a sensor on the incoming supply turns the charger down when the house is busy, and it usually avoids a supply upgrade. In an older Surbiton house we also check for a looped supply shared with a neighbour, which UK Power Networks says has to be re-planned with both households and may carry a charge.
Your installer notifies the network about both. Surbiton’s town centre is on UK Power Networks’ South Eastern Power Networks, but its London Power Networks area is about 1.5 km away, so homes near the edge of town should confirm their network with UK Power Networks’ postcode area checker. Its Smart Connect service takes chargepoint and battery forms.
VAT, grants and the kit
The two are taxed differently. Under HMRC’s VAT Notice 708/6, residential battery installations are zero-rated until 31 March 2027 and 5% from 1 April 2027, while a home charger installation is standard-rated at 20%. A quote for both on a Surbiton house should show them as separate lines, so the 0% and 20% rates are each applied to the right equipment.
On grants, owners of houses get nothing towards a charger. Renters and people who own and live in flats can get 75% of the cost, up to £500 per socket, with private off-street or allocated parking. The claim must be made through an OZEV-authorised installer; tell us your situation at the quote stage, and see our guide to who qualifies for the chargepoint grant. For a battery, the income-linked Warm Homes: Local Grant funds one only alongside solar panels.
The battery systems in our own job photos are EnSmart, and the charger we fit is the EnSmart SmartBee-M. In a tall Victorian Surbiton house, where the meter position can mean a long cable run to the drive, the survey also decides where each unit sits. A standard grid-connected battery does not keep the house or the charger running in a power cut unless backup is designed in.
Flats in Surbiton
29.8% of Kingston households live in purpose-built flats and 6.5% in converted or shared houses (Census 2021). In a flat, a battery and a charger each need somewhere to go and the freeholder’s agreement, and the battery is the harder of the two to place. Our battery storage in Surbiton page covers where one fits, and our guide to home EV charger installation covers the charger itself.
Sources: Energy Saving Trust, Battery storage (updated 19 August 2026); European Commission JRC, PVGIS 5.3 (4 kWp, 35°, due south, 14% losses, PVGIS-SARAH3 2005 to 2023), run 15 October 2026; DfT and DVLA, VEH0142 licensed plug-in vehicles by local authority, private keepers, 2026 Q2 and 2025 Q2 (published 23 September 2026); DESNZ, Renewable electricity by local authority 2014 to 2025, published 29 September 2026; HMRC VAT Notice 708/6; GOV.UK, Warm Homes: Local Grant (DESNZ guidance updated 2 July 2026); GOV.UK, Changes to electric vehicle chargepoint grant schemes from 1 April 2026 (updated 7 July 2026); Electric Vehicles (Smart Charge Points) Regulations 2021; UK Power Networks licence boundaries (UKPN Open Data, December 2024), fuse upgrades and looped supplies, and Smart Connect (read 15 October 2026); ONS Census 2021, TS044, Kingston upon Thames (Nomis). Ratios, hours and per-day figures are our arithmetic.