Winter range: how much you actually lose

Winter range loss is not one phenomenon but the sum of three independent effects. First, a cold cell gives up less energy and takes it back more slowly. Second, the cabin has to be heated, and there is no engine waste heat to do it with. Third, driving resistance rises, because cold air is denser, tyres roll harder and snow drags.

The three behave differently. The cell loss is largest at the start of a journey and fades as the battery warms. Heating draws a roughly constant power regardless of speed — so in town it weighs far more heavily in percentage terms than on the motorway. Driving resistance, by contrast, grows with speed and hits motorway journeys hardest.

Keep them apart and you also see why two drivers of the same model report entirely different figures. One drives ten kilometres to work and heats a cold car the whole way; the other does two hundred in one go and has the heating on a low setting after twenty minutes.

In a lithium-ion cell, ions travel through a liquid electrolyte from one electrode to the other. Cold makes that electrolyte more viscous and slows them down. The result is higher internal resistance: for every amp that flows, more voltage is dropped inside the cell itself, and that voltage becomes heat instead of motion.

So cold reduces not only the energy you can take out but also the power available. Many cars limit acceleration at low temperatures, and nearly all limit regeneration: a cold cell must not be charged at high current, or metallic lithium plates out on the anode — a process that damages the cell permanently. That is not a software fault, it is protection.

The effect is reversible. Once the cells reach their operating window — roughly twenty to forty degrees — capacity and power come back. The battery does not have less capacity in winter; it simply will not release it while cold.

A combustion engine throws away about two thirds of its energy as heat; some of that warms the cabin for free. An electric drivetrain is efficient and therefore produces little waste heat. Whatever warms the cabin has to come out of the battery.

A resistive heater turns one kilowatt-hour of electricity into exactly one kilowatt-hour of heat. Warming a cold cabin it draws several kilowatts, less once it is warm. What matters is the ratio to traction power: if you average six kilowatts to move in town and three to heat, you lose half your range. At twenty-five kilowatts on the motorway, the same three kilowatts cost you about a tenth.

A heat pump moves heat rather than making it and delivers more than one kilowatt-hour of heat per kilowatt-hour of electricity. How much more depends on the temperature difference it has to bridge — in mild frost the gain is substantial, in hard cold it shrinks. Whether the option price pays back is a question of its own.

Aerodynamic drag is proportional to air density, and density rises as temperature falls. Between a mild autumn day and a hard frost lies a difference of several per cent — at motorway speed, where drag eats most of the power, that is directly measurable.

Then there is rolling resistance. Winter tyres use a softer compound and a coarser tread; both increase hysteresis losses. Cold air in the tyre also means lower pressure — pressure drops noticeably for every ten degrees of cooling, and a soft tyre rolls worse. Slush and wet roads come on top.

This part of the loss hits combustion cars just as hard. It stands out on an electric car only because the remaining range sits in front of the driver in kilometres, while nobody compares a petrol car's January consumption with its July figure.

There is no single figure, and anyone who gives one has a particular driving profile in mind. As an order of magnitude — and explicitly no more — winter loss on mixed roads in moderate frost runs between a fifth and a third of summer range. On short urban trips with a cold car it can be considerably more; on long motorway runs in a mild winter, considerably less.

Two numbers describe your own situation better than any rule of thumb. The first is consumption per hundred kilometres, measured over a week in January and a week in July. The second is the longest trip you have to do without stopping to charge. Only the ratio between them tells you whether winter is a problem at all.

For most commuters it is not. Drive forty kilometres a day and charge overnight, and winter shows up only as a higher electricity bill. It becomes a problem where range was already tight in summer.

The largest single item — warming the cabin — can be taken out of the journey. If the car is on the cable and heats before you leave, that energy comes from the socket and not from the battery. The car starts warm, the windows are clear, and consumption over the first ten kilometres looks like summer.

Some cars precondition the battery at the same time. That is the second lever: a battery inside its operating window gives full power, regenerates immediately and charges on the road at the rate it was built for. Entering a fast charger into the navigation triggers exactly that preheating on many cars — which is why it is worth entering the stop even if you know the way.

After that come the small things, and they add up:

A cold battery not only accepts less power, it accepts it much later. At a fast charger that means the display shows a figure far below the data sheet and only rises once the charging current itself has warmed the cells. In hard cold a stop can therefore take twice as long as the same stop in summer.

That gives a simple rule for long trips: drive the last stretch before the stop briskly and enter the stop in the navigation so preconditioning starts. A car that arrives with a warm battery stands for less time than one that has to warm up at the charger.

At home it makes no difference. At eleven kilowatts the current is small enough that temperature barely limits anything — the night is long enough anyway. But anyone without a connection of their own who relies on fast charging through the winter pays for it twice: once in kilowatt-hours, once in time.

Plan with winter range, not with the official figure. Take the brochure number, subtract a third and check whether what is left covers your longest regular journey. If it fits on that basis it fits all year. If it only fits in summer you will be unhappy in January, however good the car is otherwise.

Two options are worth more in winter than in summer: a heat pump and a battery heater with preconditioning. Both were extra-cost on many models and neither can be retrofitted. On a used car they therefore belong on the list of things to settle before the test drive.

And the practical advice: take the test drive on a cold day if you can arrange it, and drive the route you actually drive. Half an hour at three degrees tells you more about everyday usability than any range figure.