The obvious idea, once you own an electric car, is to buy a home battery big enough to fill it. In Borehamwood, as almost everywhere, that is the wrong way round. A battery is sized to what the house uses in the evening; the car is charged by a smart charger in the cheap overnight hours. The numbers below show why, and they use only published figures plus our own arithmetic.
More Hertsmere households are facing the question. DVLA counts 3,939 privately kept plug-in vehicles across the borough at the end of June 2026, up from 3,069 a year earlier, a rise of about 28%. The figure covers all of Hertsmere, not Borehamwood alone, and counts cars where the keeper lives, not chargers. For the charger side of this, see our page on EV charger installation in Borehamwood.
Three sizes side by side
Start with the house. Ofgem’s typical domestic consumption value, from 1 July 2026, is 2,500 kWh a year for a medium household, about 6.8 kWh a day. The Energy Saving Trust, in its battery storage guidance updated 19 August 2026, says a typical home system might be 10 kWh, and that there is no exact formula for sizing one. In the Borehamwood built-up area, 26.8% of households live in semis and 9% in detached houses (Census 2021), the homes most likely to have the drive, the wall space and the roof to consider all three. Now the car. A 60 kWh battery is a common size, and it is the one we use in our cost examples. Put the three together and the mismatch is plain: a 10 kWh home battery holds about a day and a half of typical household use, while one full 60 kWh car charge is closer to nine days of it (our arithmetic). A home battery big enough to fill the car every night would be several times the Trust’s typical size, and it would still have to be refilled from somewhere.
What the battery is actually for
A home battery earns its place by moving electricity from one part of the day to another. On a smart tariff it can charge in the overnight window and run the house through the evening, when a time-of-use tariff charges more. With panels on the roof, it can also hold some of the midday output for later. The Energy Saving Trust puts a typical lifespan at about 10 to 12 years, so it pays to size it for the evenings you actually have, from your own meter readings. In a Borehamwood December, when PVGIS gives a 4 kWp roof only about 4.4 kWh a day, the battery’s evening supply comes almost entirely from the overnight window. The car fits round that. Every new home charger sold in Great Britain has had to be smart since 30 June 2022, and the regulations behind that rule define weekday peak hours as 8am to 11am and 4pm to 10pm, so a new charger comes set to avoid them. The car fills overnight; the battery covers the evening peak. They share the off-peak window rather than competing for one big store.
Summer surplus: car or battery, not both
On a Borehamwood roof, PVGIS gives a 4 kWp south-facing array about 476 kWh in June, roughly 15.9 kWh a day. After the house’s 6.8 kWh, about 9 kWh is left on an average June day (our arithmetic). That is close to what a 10 kWh battery holds, or roughly an hour and a quarter of charging at 7 kW. In practice, on a sunny day the surplus goes to one or the other. If the car is out during the day, the battery takes it; if the car is at home and the charger setup can follow the solar output, the car can take some.
In December, the same array makes about 136 kWh, about 4.4 kWh a day, which the house uses itself. In winter, both the battery and the car rely on the overnight grid. Our page on battery storage in Borehamwood covers how a battery is sized and connected in more detail.
The supply has to carry both
A 7 kW charger draws 32 A continuously, and most homes have a 60 A, 80 A or 100 A main fuse. A battery charging overnight adds its own load in the same hours as the car. The survey adds the two together with whatever else may be running, and load management, a current sensor on the incoming supply, lets the charger slow itself so the total stays within the fuse. UK Power Networks says it can upgrade a main fuse from 30 or 60 A to 80 or 100 A where that is needed. Borehamwood town centre is well inside UK Power Networks’ Eastern Power Networks area, about 10 km from its London area, and the installer notifies UKPN of the new equipment. The VAT treatment differs too. A residential battery installation is zero-rated until 31 March 2027, then 5%; a home charger is standard-rated at 20%, as it is not on HMRC’s energy-saving materials list. On a combined quote, each line should carry its own rate.
Flats, housing associations and space
A battery needs a wall or floor space, a cable route and, for many Borehamwood households, someone else’s consent. In the Borehamwood built-up area, 34% of households live in flats, maisonettes or apartments and 26.0% rent from a social landlord, against 17.3% across Hertsmere (Census 2021). In those homes, a battery or charger starts with the freeholder or housing association. Renters and flat owner-occupiers with private or allocated parking may qualify for a charger grant of 75% of the cost up to £500 per socket; our guide to who qualifies for the EV chargepoint grant explains it, and claims go through an OZEV-authorised installer, so tell us your situation at the quote stage.
The plain summary
Size the battery to the house and let the charger look after the car; in a WD6 flat or housing association home, start with the building owner. The batteries in our own job photos are EnSmart, and the charger we fit is the EnSmart SmartBee-M; our home EV charger installation page explains the charger. Bring a year of meter readings to the survey and we can show what a battery would do for your evenings, separately from what the car needs.
Sources: Department for Transport and DVLA, VEH0142 licensed plug-in vehicles by local authority, Hertsmere, privately kept, 2025 Q2 and 2026 Q2 (published 23 September 2026), change our arithmetic; Energy Saving Trust, Battery storage (last updated 19 August 2026); Ofgem, Typical Domestic Consumption Values from 1 July 2026; The Electric Vehicles (Smart Charge Points) Regulations 2021, regulation 10; European Commission JRC, PVGIS 5.3 (PVGIS-SARAH3 2005–2023; 4 kWp, 35° tilt, due south, 14% losses, building-mounted), Borehamwood town-centre point, run 15 October 2026, daily figures our arithmetic; UK Power Networks, fuse upgrade guidance; UK Power Networks Open Data and NESO licence boundaries; HMRC, VAT Notice 708/6; ONS, Towns and cities: characteristics of built-up areas, Census 2021 (tables 5c and 6c, Borehamwood); ONS Census 2021 TS054, Hertsmere; GOV.UK, Changes to electric vehicle chargepoint grant schemes from 1 April 2026 (updated 7 July 2026).