Everyone knows winter shortens an electric car's range, and that a heat pump softens the blow. Far fewer people realise that a heatwave costs range too. The loss is smaller than a hard frost, but on a scorching day a car can drop a fifth of its range, and this time the heat pump that rescues you in January is no help at all. Here is why heat costs miles, how much, and what to do about it.
The short answer. Yes, hot weather cuts EV range, typically by around 10 to 25 per cent in a heatwave compared with a mild day, mostly from running the air conditioning and from the battery's own cooling system. The hit is smaller than deep winter's, because the battery itself works happily when warm. Unlike winter, a heat pump does not save you, since in the heat every electric car leans on the same air-conditioning compressor. Pre-cool the cabin while plugged in, park in the shade, and avoid sitting at 100 per cent in extreme heat.
Heat cuts range, but less than cold
An electric car is happiest in mild weather, somewhere around 20 degrees, where neither heating nor cooling is doing much work. Push the temperature up into the thirties and the range falls, just as it does in the cold, but by less. The reason is that the battery itself is content when warm; it gives up and takes on energy readily, which is the opposite of its sluggishness in the cold. So the heatwave penalty comes almost entirely from the extra loads the hot weather creates, not from the battery struggling, which is why it is a milder effect than the double hit of a cold battery plus cabin heating you get in winter, set out in the EV charging in winter guide.
Why a hot day costs you miles
Two things drain the battery in a heatwave. The first is the air conditioning, which on a very hot day runs hard to keep the cabin bearable, and that cooling energy comes from the battery that would otherwise be driving you forward. The second is the battery's own thermal management: modern electric cars actively cool the pack in extreme heat to protect the cells, and running that cooling draws power too. Together these are what trim your range. There is a silver lining, though, that petrol drivers do not get: an electric motor produces far less waste heat than an engine, so on a hot day the cabin starts off less brutally hot and the air conditioning has a slightly easier job than it does in a petrol car sitting behind a roasting engine bay.
How much range you lose
As with winter, the figure is a range rather than a single number, depending on how hot it is and how hard the air conditioning works. A warm day costs little; a full heatwave with the cooling running flat out can take a fifth or more off your usable range. The table sets the heat penalty against the familiar winter one for scale.
| Conditions | Typical range vs a mild day |
|---|---|
| Mild day, around 20C | baseline, the best you will see |
| Hot day, around 30C, air con on | ~10 to 15% less |
| Heatwave, 35C and above, cooling hard | ~15 to 25% less |
| Hard winter frost, for comparison | ~25 to 30% or more less |
Indicative figures; the exact loss varies by car and conditions. The pattern holds across studies: heat cuts range, but a hard frost cuts it more. The loss shows up as a lower miles per kWh figure, so the same charge takes you less far.
Why a heat pump will not save you in summer
This is the part that surprises people. In winter, a heat-pump-equipped car claws back a big chunk of the range a cold day would otherwise cost, because the heat pump warms the cabin far more efficiently than a plain electric heater. A heatwave is a different problem. Cooling the cabin is done by the air-conditioning compressor, and every electric car has one of those whether or not it has a heat pump, so in the heat they are all on much the same footing. The heat pump is a winter saviour, not a summer one. In fact some cars with heat pumps show slightly larger range loss in extreme heat than those without, because makers tune the system around the bigger prize of cold-weather efficiency. If you bought a heat-pump car expecting it to rescue your range in August too, this is the reality: in the heat, you are leaning on the air conditioning like everyone else.
Rapid charging can slow in the heat too
Heat does not only cost range, it can slow charging. Just as a cold battery limits how fast it will charge, a battery that is already hot, from a long fast motorway run in a heatwave, may have its rapid-charging rate held back while the car cools the pack to a safe temperature. So a mid-journey rapid charge on a blazing day can take longer than you expect. Home charging is barely affected, because the slow overnight rate sits well within what the battery can handle at any sensible temperature.
The bigger issue: heat ages the battery
The temporary range dip is the least of it. Sustained high temperature is one of the things that ages a lithium battery fastest, more so than cold, so the heat question is as much about long-term battery health as about today's range. The practical steps are simple. Park in the shade or a garage whenever you can, so the pack is not baking in the sun all day. Avoid leaving the car sitting at a full 100 per cent charge in extreme heat, since a full battery held hot is the hardest case of all; for everyday use a charge limit of around 80 per cent is kinder. And use slow home charging rather than repeated rapid charging in hot spells, which is gentler on a warm pack.
How to limit the range loss
The single most useful habit is the summer twin of winter preconditioning: pre-cool the cabin while the car is still plugged in. Cooling the car down from the mains before you set off, rather than from the battery once you are moving, means you start your journey in a comfortable car with a battery at a sensible temperature, having spent no range on the initial blast of cooling. Most electric cars let you schedule this to finish around your departure time, the same feature covered for warming in the best time to charge guide. Beyond that, park in the shade and use a windscreen sunshade so the cabin is not an oven to begin with, lean on ventilated or cooled seats where the car has them rather than chilling the whole cabin, and once the car is cool let the air conditioning tick over gently rather than running at maximum. Each of these trims the cooling load, and with it the miles the heatwave takes.
The bottom line
Hot weather cuts an electric car's range by roughly 10 to 25 per cent in a heatwave, mostly through the air conditioning and the battery's cooling, which is real but less than a hard winter's loss because the battery itself likes the warmth. The catch is that a heat pump, the hero of winter range, does nothing for you in summer, when every car relies on the same air conditioning. Pre-cool while plugged in, park in the shade, keep the charge off 100 per cent in extreme heat, and the heatwave becomes a manageable dip rather than a worry, for both your range today and your battery's life over the years.