Charging explained: what an electric car actually asks of you

An electric car charges in three places: home, work, public. They are not interchangeable. Home charging is slow, cheap and invisible — plug in, go to bed, the car is full. Public rapid charging is fast, expensive, and something you stand next to.

The first of the three decides whether an electric car suits you at all. A driver with a wallbox at home almost never touches a public charger except on a long trip. A driver without one pays public prices for every kilometre. Same car, entirely different ownership.

So answer the parking question before you compare models. The finder asks it directly — home, work, street, or unsure — because it decides which of the 22 electric cars here are worth showing you, and whether any of them are.

A battery stores direct current. The grid delivers alternating current. Something between the socket and the cells has to convert one into the other, and where that happens is the whole difference between the two kinds of charging.

On AC charging — a domestic socket, a wallbox, most street posts — the converter sits inside the car. It is the onboard charger, a box with a weight and a cost, sized for overnight use: commonly 7.4 kW single-phase, 11 or 22 kW on three-phase. That box, not the battery, is the ceiling. Plug a 7.4 kW car into a 22 kW post and it draws 7.4 kW.

On DC rapid charging the conversion happens in the charger instead. The cabinet at the roadside is the size of a wardrobe because it holds the hardware the car cannot carry, and it feeds the battery directly, bypassing the onboard charger. It is not a better cable. It is a different architecture.

Home charging is therefore slow by design rather than by fault. Nobody wants a wardrobe-sized rectifier in the boot, and a car parked for eight hours has eight hours to spend.

Those are arithmetic: power multiplied by time. A domestic socket at 230 volts and 10 amps is 2.3 kW, and eight hours of that is 18 kWh. A wallbox at 32 amps is 7.4 kW.

Now put a car on the end of the cable. The electric cars here quote ranges from 225 km to 655 km. As a working rule of thumb, a modern electric car uses 15 to 20 kWh per 100 km — more in winter, more at motorway speed, less around town. Drag adds to it — a roof box, a headwind, above all a trailer, which is a problem of its own .

Run that backwards. A single-phase wallbox puts in roughly 59 kWh overnight, which at 17 kWh per 100 km is about 340 km added between bedtime and breakfast. Even a domestic socket adds around 100 km a night, and very few drivers cover that in a day. Home charging is only slow next to a petrol pump, which is the wrong comparison: you are not waiting for the car, you are asleep.

1. 1

   Count a normal week, not a big one

   Add up the kilometres you actually drove in the last seven days. Most drivers land well below the range of the cars they are looking at.

2. 2

   Find the worst trip you make regularly

   The longest journey between two charging opportunities sets the range you need, not your annual mileage. A 400 km run to family four times a year is a rapid-charging question, not a range one.

3. 3

   Decide what unsure means

   If you do not know whether a wallbox can be fitted where you park, answer that before you get attached to a car. It is a question for an electrician, and if you rent, for a landlord too.

A lithium-ion cell accepts a large current while it is fairly empty and less as it fills. Early on the charger holds a high, roughly constant current; as the cells approach full their voltage rises, the current is cut back to stay inside safe limits, and power falls with it. Pushing hard at a high state of charge risks plating metallic lithium onto the anode, which permanently removes capacity. The taper is protection, not weakness.

The consequence is well known: on most cars the last 20 per cent takes about as long to fill as the first 80. A run from 10 to 80 per cent might be twenty to forty minutes on a fast enough post. Going on to 100 per cent can add as long again, for a fifth of the energy.

So on a long trip, do not fill the battery. Take it to 80 per cent, drive, and stop again. Two short stops beat one long one, and you spend the taper driving rather than standing. Fill to 100 only when the next charger is far away, or overnight on AC, when time costs nothing.

• Temperature. A cold battery accepts less current. Most cars precondition the pack if you set the charger as a navigation destination, often the difference between a fast stop and a slow one.
• How full it is on arrival. Turning up at 10 per cent buys you the steep part of the curve; turning up at 60 per cent means paying for the slow part.
• The car, not the post. A 350 kW charger cannot make a car accept more than it accepts, and peak power lasts minutes rather than a whole session.

Here is the honest part. If you park on the street and cannot run a cable to the car, electric ownership today is a worse deal than the brochures suggest, and in some cases it is simply the wrong answer.

What exists varies enormously by city. Some have lamp-post and bollard chargers on residential streets — slow AC posts, and good ones if you can reliably get a space near your door. Some have nothing. Workplace charging solves the problem outright, and it is worth asking about before you assume otherwise. Topping up during errands you already run is a real strategy for a low-mileage driver. Building a weekly trip whose only purpose is to sit at a charger is not.

Two costs follow from having no supply where you park. The first is money: public charging is billed at rates the network sets, consistently above domestic electricity, so the running-cost advantage can disappear. Look up the actual price per kWh near you first. What a car costs to run has the rest of the arithmetic; monthly running costs here span €72 to €265.

The second cost is time, and it is yours. An hour at a rapid charger once a week is fifty hours a year that a driveway would have handed straight back.

If you have no reliable overnight charging and drive a lot, a hybrid does most of what people want from electrification while asking nothing of your parking. A plug-in hybrid is the worst of both worlds when it is never plugged in and one of the best when it is — a parking question too, not an engine question.

Batteries degrade. Nothing stops that. A few habits slow it down, and none of them cost anything.

• Use AC for daily charging and DC for journeys. Rapid charging daily is harder on a pack than doing it occasionally, and heat is the mechanism.
• For daily use, many manufacturers suggest keeping the charge between 20 and 80 per cent. Set the limit in the car so it stops there.
• Charge to 100 per cent the night before a long drive, not days ahead. Sitting at a very high state of charge, especially in heat, does the damage; arriving full and leaving does not.
• Do not leave the car near empty for weeks, and park in shade in summer. Temperature matters more than most charging decisions you make.

Where the advice genuinely splits

The 20-to-80 rule came out of experience with nickel-rich chemistries and is not universal. Cars using lithium iron phosphate cells — common at the cheaper end — often carry the opposite instruction: charge fully and regularly, because the state-of-charge reading drifts and needs a full charge to recalibrate. That is a real technical disagreement rather than a marketing one, and the decision rule is simple: the handbook for your car beats any general advice, this guide included.