EV charging at home explained: from socket to 2p a mile
Charging an electric car at home is where most of the savings of going electric come from, and where most of the confusion lives. The technology is simpler than the jargon suggests; the money is mostly about when you charge, not how fast.
The one-sentence version
A home wallbox refills the car overnight, and on a cheap off-peak tariff that works out around 2p a mile against roughly 14p on petrol, so the more of your charging you do at home off-peak, the bigger the saving.
The three charging speeds
- Slow (a three-pin plug, around 2.3 kW). A trickle, fine as a backup but adds only a few miles an hour.
- Fast (a 7 kW home wallbox). The standard home charger. It adds roughly 25 to 30 miles of range an hour, enough to fully refill almost any car overnight. Most UK homes have a single-phase supply, which caps a home charger at 7 kW; a few with three-phase can fit 22 kW.
- Rapid and ultra-rapid (50 to 350 kW, public). DC chargers that bypass the car's onboard charger to refill in tens of minutes on a journey. Convenient but far more expensive per unit than home charging.
AC, DC and the onboard charger
An expert point that explains the speeds: the battery stores DC, but the grid and your home supply AC. Home and "fast" chargers supply AC, and the car's built-in onboard charger converts it to DC, which is what limits home charging to 7 kW (or 11/22 kW with three phase). Rapid public chargers convert to DC themselves and feed the battery directly, which is why they are so much faster. So "7 kW" is a limit of the car and supply, not just the box on the wall.
Why off-peak tariffs change everything
A car is a large, flexible, overnight load, which is exactly what time-of-use tariffs reward. Dedicated EV tariffs offer cheap overnight windows as low as around 7p per kWh, a fraction of the daytime rate. At 7p and a typical efficiency of 3 to 4 miles per kWh, a mile costs roughly 2p. The same charging on the standard rate, or worse at a public rapid charger, costs several times more. The single best thing an EV owner can do is move charging to the off-peak window, which a smart charger or the car's timer does automatically.
Smart charging, and where it is heading
A smart charger talks to the grid or your tariff and schedules charging for the cheapest, greenest hours without you thinking about it. Pair it with solar and it can soak up your midday surplus instead of exporting it cheaply. The frontier is vehicle-to-grid (V2G) and vehicle-to-home (V2X): with a bidirectional charger and a compatible car, the car's large battery can discharge back to your home or the grid at peak, effectively a home battery on wheels. It needs specific hardware and a supporting tariff, and it is rolling out through bundled packages rather than being universal yet.
Efficiency: miles per kWh
The EV equivalent of miles per gallon is miles per kWh. Most cars manage 3.0 to 4.0, more in mild weather and gentle driving, less in cold weather (the battery and cabin heating both draw power) and at motorway speed. Knowing your real figure lets you translate any tariff rate into pence per mile and compare honestly with petrol.
The practical install
A 7 kW wallbox costs roughly £800 to £1,100 fitted. The installer checks your main fuse and consumer unit can take the extra load (load management can throttle the charger if needed), fits the required protective devices, and notifies the network operator. Renters and flat owners without a driveway may be able to claim a grant toward a charge point. Siting near the parking spot and the consumer unit keeps cabling simple and costs down.
Where to go next
Estimate your home-charging cost and saving with the EV charger calculator, read the practical detail in EV charging at home, and see how the right tariff stacks up in fixed vs tracker vs variable.
Battery care: why 80% is the everyday target
An EV battery lasts longest if you avoid keeping it at the extremes. Day to day, charging to around 80% and not letting it sit near empty is gentler than always filling to 100%; most cars let you set a charge limit and will hit 100% only when you ask for a long trip. Rapid DC charging is convenient but generates more heat and, used as the only method, ages a battery faster than steady home charging, another reason home charging is the cheaper and kinder default. Cold weather temporarily reduces range and slows rapid charging, because the cells perform best when warm; many cars pre-condition the battery on the way to a rapid charger to compensate. Modern EV batteries are warrantied for around 8 years or 100,000 miles to a minimum capacity, and real-world degradation has proved slower than early fears suggested.
Public charging: networks, connectors and costs
Away from home the picture is different. Almost all modern EVs use a Type 2 socket for AC charging and CCS for rapid DC, so connector compatibility is rarely an issue now. Public charging spans slow on-street posts, destination chargers at shops and car parks, and rapid or ultra-rapid hubs on main routes. The catch is cost: rapid public energy can cost several times the home off-peak rate, so the economics of an EV depend heavily on the share of charging you do at home. For most drivers the pattern that works is cheap overnight home charging for daily mileage, with public rapids used only to top up on longer journeys.