Electric car range almost halves when driving in heatwave temperatures

A new study has revealed the impact of heatwaves on the performance of electric cars – and in some instances claimed battery range can fall to almost half official figures.

While it’s relatively well known that winter conditions can have a debilitating impact on the range of EVs – due to batteries needing to reach an optimum temperature to deliver energy efficiently – an exclusive test by What Car? found sweltering heatwave temperatures can be equally range sapping, if not worse.

For its latest range assessment, the automotive title drove three popular EVs - a Citroen e-C3 Max, Kia EV3 Long Range GT-Line S and Tesla Model 3 Long Range RWD - through the ‘frying pan of Andalusia’ in Spain.

The journey, travelling over 200 miles eastbound from Seville, to Cordoba and Montoro, before heading to the south coastal region of Aguadulce, was completed in boiling ambient temperatures between 32 and 44 degrees C.

And it was the Tesla that suffered most – despite the brand’s origins in Texas, where it typically exceeds 38 degrees in the summer months.

What Car? said that while it’s rare for the UK to endure such extreme conditions, summer heatwaves recorded this year will have taken a toll on the performance of electric cars.

For the tests, all three cars were kept overnight in the same ambient air temperature, had their tyre pressures adjusted to the manufacturers' recommendation and the climate control set to 21 degrees, to ensure the driver remained comfortable, as drivers would seek to when temperatures soar in the summer months.

All three cars were left in their default driving modes with the lightest level of regenerative braking. Every EV had its battery charged to 100 per cent before setting off.

And the soaring temperatures took a big toll on the range performance of each car.

What Car? measured that the Citroen e-C3 Max (which now costs from £22,295 inclusive of the Government's 'Band 2' £1,500 Electric Car Grant discount) managed only 142 miles on a full charge - 29 per cent short of its official figure of 199 miles.

The Kia EV3 (Long Range GT-Line S costing £43,005) managed 246 miles, which is 32 per cent less than its stated 362-mile range.

But worst of all was the £44,990 Tesla Model 3 Long Range that could only cover a maximum of 244 miles in the stifling heat. This is 44 per cent down on its 436-mile official range.

When What Car? calculated overall efficiency – taking into account the amount of electricity each car required – the results turned on their head.

The e-C3 achieved just 2.7 miles per kilowatt hour (mi/kWh), the EV3 averaged 2.9mi/kWh and the Model 3 best of all with a return of 3.0mi/kWh.

However, the Citroen e-C3's already comparably short official range - which became even more restrictive due to the conditions - meant it was unable to complete the journey on a single charge, so the test team was forced to pull over in Montoro to plug into a charger.

The only 50kW public device available was already in use, meaning the assessors were forced to wait 45 minutes for another EV user to vacate the charging point for them to use it.

Charging using the 50kW device from the 3 per cent it had remaining up to 80 per cent took an hour and 14 minutes, and a further 34 minutes to reach 100 per cent. Charging the e-C3 at a UK motorway services would take far less time, with plenty of charging points to deliver the 100kW speeds the Citroen can accept.

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What Car? reviews editor, Will Nightingale, said: ‘Our extreme temperature test shows that range and efficiency plummet in very hot conditions.

‘The three EVs fell an average of 35 per cent short of their official figures, which is worse than the result we achieved our most recent winter range test and more than double the discrepancy seen in the 2024 What Car? summer range test.’

When the consumer title put 12 EVs through winter tests (in temperatures between 10 and 11 degrees C) in 2023, the real-world range fell short on average by 30 per cent compared to their official claims.

Last summer, during UK tests in temperatures between 17 and 23 degrees, the average range shortfall measure across 12 popular EVs was 14 per cent.

That said, this was a more representative summer test, reflecting conditions drivers in Britain are most likely to experience.

‘While extreme heat is still (thankfully) quite rare in the UK, the planet is undoubtedly heating up. We’ve already seen temperatures of more than 40 degrees C in the south of England and multiple heatwaves have swept the country this summer,’ Will added.

‘So, hopefully, as technology advances, EVs will become better at coping with extreme temperatures.’

The report comes as as The Telegraph calculated that people in England are walking further than ever amid soaring driving costs.

The average English person travelled approximately 10 per cent further on foot and a third further by train in 2024 than they did 20 years ago, its analysis of Department for Transport statistics found.

Meanwhile, the distance driven annually has fallen by around 10 per cent in the last decade alone, down from 5,057 miles per year in 2015 to 4,621 miles in 2024.

Miles driven dropped dramatically during the Covid-19 outbreak in 2020 due to travel restrictions, though with more employees hybrid working - and therefore commuting less - since the pandemic, average car mileage hasn't returned to previous levels.

Edmund King, president of the AA, says the cost of motoring is also having an impact, with many English drivers feeling 'priced out' of their cars thanks to taxes, rising fuel prices and measures such as Sadiq Khan’s London ULEZ.

The main reason EVs fall so short of their manufacturer claimed ranges in heatwave-like temperatures - and most real-world driving scenarios - is due to the favourable conditions used during 'official' tests.

Every type-approved EV sold in the UK must be put through the 'Worldwide Harmonised Light Vehicle Test Procedure - or WLTP for short.

All petrol, diesel and hybrid cars also complete this test to measure the CO2 emissions output and the fuel economy - or miles per gallon (MPG) - quoted in brochures.

However, these tests are conducted in controlled lab conditions, with the ambient temperature set to just 23 degrees.

Neither the air-con nor the heater is used during the assessment, which allows the electric powertrain to perform optimally without any strain from other systems.

As such, 'official' ranges are always more optimistic than drivers will see under real-world conditions.

For instance, it is the 'greenhouse effect' of heatwave temperatures on the cabin - and the need to use the air-conditioning to remain comfortable - that's a significant drain on range in the summer months.

The huge expanses of glass in any car allows the sun in but trap heat inside that radiates off the interior surfaces. This is the case even more so with models with large glass panoramic roofs, like the Teslas.

As a result, the car's air-conditioning system must work extremely hard to counter this, and that uses up energy that could otherwise be utilised to power the wheels.

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What Car? cited a US study from last year which found that the auxiliary load on an EV’s battery - mainly from using the car's heater and air-con - is greater at 40 to 46 degrees than at between -4 and 0 degrees.

Modern EVs now have 'thermal management systems', which are designed to cool the battery cells to help prevent increased degradation.

'The same study found that the propulsion load (that’s the energy needed to move the car along) is only slightly lower at 40-46deg than at 6-10deg. Batteries generally operate most efficiently with the air temperature at 20-25deg, so an EV won’t be operating in its optimum window on plenty of summer days in the UK,' the report said.

The report also highlighted that the heatwave conditions also appeared to impact charging speeds, which took longer than claimed.

For instance, a 10 to 80 per cent charge for the Citroen e-C3 should take just 48 minutes. But upping it from 3 to 80 per cent took almost half an hour longer.

However, What Car? pointed out that claimed charging speeds are rarely replicated in real world conditions.