Charging on the road: what makes up the price

What a public charger bills is made up of as many as four parts, and not every provider uses them all. The unit rate is charged on the energy taken, in kilowatt-hours. A session fee applies once per charge, whatever the amount. A time or idle fee is charged by duration, often only after a certain period. A roaming surcharge is added when you charge at a point that does not belong to your provider.

Which of these dominates depends on your own behaviour. Charge rarely but heavily and you mostly pay the unit rate. Top up often and briefly and you mostly pay session fees. Have lunch at the charger and you mostly pay for time. A tariff that is cheap for one driver is the most expensive for another.

No amounts appear here, and that is deliberate: they differ by country, provider, location and moment, and they change constantly. What does not change is the composition — and with it you can check any offer.

There are two ways to a charge. Paying directly — often called ad hoc — starts the session with no contract, by card, app or a code on the unit. That is convenient and usually the most expensive route, because the operator has no contract customer in front of it and prices accordingly.

The second is a contract with a charging provider. It usually brings lower unit rates and one bill across many networks, often at the cost of a monthly fee. The arithmetic is simple: the monthly fee divided by the saving per kilowatt-hour gives the volume above which the contract pays. Charge less than that and you are better off without one.

For someone who charges at home and only uses public points when travelling, a tariff without a monthly fee is usually right, even at a higher unit rate. For someone with no charging at home it is the other way round. That single question — where do you mostly charge? — settles the tariff choice entirely.

Behind every charging point stand two companies. One operates the point and sells the charge; the other has you as a customer and bills you. Where both are the same company, the house tariff applies. Where they are not, the session runs through a roaming agreement — and the provider that bills you adds its margin to the operator's price.

So it is worth checking the app before you stop: it normally shows the price your provider charges at that specific point, and it can differ from the price on the display. On longer journeys across borders that is the single biggest lever — the same brand of charger can be billed on entirely different terms one country further on.

The display of prices is regulated. How a price must be shown and what it may be based on is set by national price-indication and metrology rules; the relevant weights-and-measures and market surveillance authorities are responsible. If you cannot follow a bill, that is where the complaint goes.

An alternating current point is essentially a switched cable with metering. A direct current point contains all the power electronics that otherwise sit in the car: rectifier, filters, cooling, often a cooled cable. The hardware costs more, lasts less long, and has to be paid off.

Then there is the grid connection. A site with several fast charging points needs a connection comparable to that of a small industrial unit. In many countries network charges are based not only on energy drawn but also on the highest power drawn — so a site pays for peaks that may occur on only a few days a year.

And finally the site itself: land beside a motorway junction, lighting, a canopy, maintenance, payment handling. All of it sits in the price per kilowatt-hour, because there is no other line to spread it over. Charge at home and you pay none of it — that, not the energy itself, is the real reason for the difference.

Idle fees have an understandable purpose: a fast charging bay occupied by a car sitting at ninety-five per cent taking a few kilowatts is worthless to everybody else. The fee therefore manages occupancy rather than consumption.

But it lands exactly where the charging curve is already flat. Because power falls as state of charge rises, the last kilowatt-hour costs not only the most time but, under a time-based fee, the most money too. The two effects compound — which is why moving on at seventy or eighty per cent is not a matter of style but a cost decision.

The exception is charging at the destination. At an AC point overnight at a hotel or during the day at work, the curve does not matter because power is low anyway. There the idle fee — if there is one — is the only reason to move the car in the morning.

What is billed is what passes the meter, not what reaches the battery. In between lie losses, and they are not small. Charging on alternating current, the onboard charger works well below a hundred per cent efficiency; some energy becomes heat. The lower the charging power, the more the car's own baseline consumption weighs — at a domestic socket the percentage loss is largest.

On direct current the onboard charger drops out, but other items appear: conditioning the battery, cooling it during the charge and, in summer, air conditioning the cabin if the driver stays in the car. That energy goes through the meter as well.

In practice: the consumption the car displays is systematically below what the bill shows. If you want your cost per hundred kilometres, calculate with the energy billed, not with the trip computer. The gap runs from a few per cent to more than a tenth, depending on how and at what temperature you charge.

There are no secret tariffs, but there is behaviour that measurably helps. These five points make the biggest difference:

The biggest lever comes first, and not by accident: in almost every tariff there is a multiple between your own supply and a motorway fast charger, and no amount of careful driving recovers that difference.

Two properties of the car act directly on charging costs. The first is consumption: it decides how many kilowatt-hours you have to buy at all. The second is charging power: it decides how long the car occupies a point that bills by time or applies an idle fee.

The third property is less obvious and just as important day to day: the ability to take full three-phase alternating current. A car that pulls eleven kilowatts at an ordinary AC point gets by on the cheap chargers. One that only manages single-phase there will fall back on direct current — the expensive route.