Why isn't my electric car charging as fast as it should?

It's a question many EV owners ask while their car is hooked up to a rapid charging point and it's taking longer than anticipated.

But while many blame the charging device, in many cases it is because the vehicle's tech is incapable of reaching the peak charging speeds they claim, according to a new study. 

New tests by Auto Express have laid bare how many popular electric cars simply don't hit the manufacturer's promised maximum charging rates.

Car makers advertise charging speeds of 150kW, 250kW or even 320kW, with estimates that EVs can top up from 10 to 80 per cent in as little as twenty minutes giving you over hundreds of miles of range to get you back on the road.

But the joint test between in partnership with charging network Gridserve saw 10 well-known EVs hooked up to a dedicated 350kW-capable devices - and only a couple managed to hit the peak charging speeds advertised.

Here's how different models fared...

How the cars were charged – the control variables

Under controlled conditions the 10 cars were charged using a Gridserve ultra-rapid charger capable of going up to 350kW. 

It was verified by Gridserve engineers that they were functioning at full power, meaning the results reflect the car's own software and battery management systems, not the infrastructure.

Each car was charged from similar starting levels (around 10 to 15 per cent battery) in ambient temperatures of 13 to 14°C – just below the ideal range.

No battery preconditioning took place (we'll expand on battery conditioning later) to simulate the kind of public charging session many drivers experience day-to-day.

Auto Express then recorded how long it took to add 60 per cent charge, the average charging speed during this period and the time taken to charge from 80 to 100 per cent.

Do EVs reach peak charging capacity? 

10. Tesla Model Y – 58% of claim

Price from: £44,990

Tesla was one one of the first manufacturers to bring in sophisticated rapid charging. In fact, the Tesla Supercharger network is the largest global, fast charging network in the world with 70,000+ Superchargers.

And it's been making EVs since 2008, so hi-tech battery management is something the Elon Musk owned brand knows well.

So, it might come as a surprise to see the Model Y performing the worst. Tesla says this the Y's poor performance was because the battery wasn't pre-conditioned for the test but this was the case for all cars in the test – and some of them were able to achieve maximum rates or close to.

The Tesla Model Y has a claimed peak charging rate of 250kW but only managed a peak charging rate of 145kW, and that was for just one minute. Auto Express says it was 'a huge shock' to see that the Y 'wasn't able to achieve anything close to what Tesla claims during the test'.

It took 30 minutes to charge the battery from 14 per cent to 60 per cent and 93 minutes to charge to 100 per cent.

The Model Y's 75kW battery charged on average at 103kW.

Auto Express said: 'Tesla has a pretty sophisticated battery-management system, so tends to reach peak power quickly – although this didn't get close, nor hold it for very long.'

9. Citroen e-C3 – 69% of claim

Price: from £20,595

The Citroen e-C3 is a cheap EV that promises to get families from A to B without much fuss or frills, and its charging reflects this.

The e-C3 only achieved 69kW speed despite claiming peak charging of 100kW.

The 44kWh battery EV maintained this peak speed for three minutes, before it dropped badly. In the end it took 34 minutes for the e-C3 to go from 15 per cent to 60 per cent charge and took 91 minutes to get to 100 per cent.

The average rate of charge was 43kW – significantly below the 100kW claimed rate.

Auto Express said: 'This example is definitely in the simple category – a cheaper car means a cheaper system.'

8. Peugeot e-3008 - 76.9% of claim

Price from: £46,060

The e-3008 has a claimed peak charging capacity of 160kW for its 73kW battery, but the Auto Express test found that it only reached 123kW which it maintained for three minutes.

Auto Express said it was 'one of the more disappointing performers' in the test as it took 10 minutes to reach its peak rate.

For most of the e-3008's charge cycle it spent very little time above 100kW.

Starting at an initial charge of 16 per cent, it took the e-3008 38 minutes to reach 60 per cent and 124 minutes to reach 100 per cent – the longest time to reach a full battery of any models tested.

Auto Express said: 'After ramping up, it drops off a cliff after. It didn't get that near the maximum rate, so Peugeot are probably overstating what it can do.'

7. BYD Seal – 82% of claim

Price from: £45,705

BYD is famous for its Blade Battery and out of this world fast charging, which its 'flash chargers' coming this year. So big things were expected from the Seal.

With a claimed charging peak of 150kW, the Seal hit a 123kW actual high during the test, a difference of -27. But it maintained it for five minutes – the longest maintained maximum speed of any EV in the test.

From 15 per cent initial charge to 60 per cent charge took 32 minutes with the 100 per cent charge taking 88 minutes. This is because BYD has pre-programmed the car to drop to 48kW at the 85 per cent mark.

The average charge speed was 104kW, and it refused to get to the full 100% instead cutting off from the charger at 99 per cent, with no explanation available from BYD Auto Express said.

Auto Express experts commented: 'After a slightly out-of-control start, it appears very contained after that, maintaining a consistent rate of charge until it throttles back down.'

6. Renault 5 – 87%

Price: from £21,495

The retro Renault 5 has been a smash hit, but the EVs rapid charging isn't quite so stella.

Despite its sophisticated battery management system, the R5 only hit 87kW – 13kW below the modest maximum stated by the brand.

It held it only the 87kW speed for two minutes, averaging speeds of 65kW for the duration of the charge.

Charging from its initial state of 11 per cent to 60 per cent took 26 minutes, while charging to 100 per cent took an hour.

Auto Express said: 'The Renault may be an inexpensive EV like the Citroen, but it's doing a better job in its battery management – although, it doesn't sustain power for long.'

5. Porsche Taycan – 88.1%

Price: from £88,200

The Taycan's 97kWh battery theoretically charges to 320kW speeds, and the end result wasn't too far off that.

It averaged a charge rate of 243kW, but crucially a peak of 282kW – a difference of –38kW. 

Porsche impressed Auto Express experts with its ability to never dip below 50kW speeds, even towards the end, and to rapidly charge such a huge battery cell so quickly.

Starting at an initial state of 14 per cent charge and hit the 60 per cent charge mark in 15 minutes.

By total time it took to reach 100 per cent, Porsche came out the winner, managing a full charge in 26 minutes – pretty impressive.

Auto Express says the Taycan 'is a good example of how to optimise a car to get as much charge in as possible in a short space of time'.

4. Kia EV3 – 94.8%

Price: from £33,005

The EV3 has a claimed peak charging rate of 135kW but managed to hit 128kW – for two minutes.

The EV3 would be awarded A* in A-Level results – if EV peak charging results were a thing - for hitting over 94 per cent of its claimed peak charging capacity.

The circa £36k EV charged from its 16 per cent initial charge state to 60 per cent in 27 minutes.

Auto Express found the car averaged 117kW during the test to 60 per cent charge, which isn't too far away from its 135kW claimed speeds.

The total charge time to 100 per cent took 55 minutes with Auto Express finding it added around 50 per cent charge in around 20 minutes.

Auto Express said: 'Interesting example of how the manufacturer has optimised the system for getting as much in as quickly as possible at the expense of a longer experience.'

3. Toyota bZ4X – 98%

Price: from £36,995

Toyota's all-electric SUV would also be awarded an A* in A-Level results.

The £42k-plus EV should ultra-rapid charge up to 150kW, and while it didn't quite get there in the test it was very close.

It achieved a maximum charging speed of 147kW –just shy of the peak.

The bZ4X's 64kWh charged at an average rate of 96kW and went from the initial 14 per cent state-of-charge to 60 per cent in 26 minutes.

Although Auto Express said the bZ4X's charging got sluggish at the end, it 'doesn't staircase up and is updating its charge current every few seconds to get the best it can'.

2. Ford Capri – 100%

Price: from £41,485

The Ford Capri might be a contentious car, but its rapid charging is impressive. It's one of only two EVs that delivered its promise peak charging capacity.

Ford claims that its 79kWh battery Capri can peak charge 187kW and it turns out that's bang on. 

As well as matching the maximum stated by Ford, the Capri stayed about the stated maximum charge for eight minutes. Over the duration of the 60 per cent top-up it averaged well over 150kW.

It went from an initial nine per cent charge state to 60 per cent in 20 minutes and averaged a charge rate of 154kW.

The peak of 187kW was achieved for two minutes.

Auto Express called it 'a fairly sophisticated system that's constantly trying to optimize the charge performance against thermal limits'.

1. Volkswagen ID.7 Tourer – 100% 

Price: from £51,795

Germany ties with America in the rapid charging head-to-head.

The Volkswagen ID.7, like the Ford Capri managed to hit the promised peak charging speed.

The VW ID.7 sticker that says 200kW charging is not about to be crossed out: it hit that speed for three minutes in test.

The 86kWh battery went from an initial state-of-charge of 12 per cent to 60 per cent in 21 minutes. It averaged a charging rate of 156kW and took 35 minutes to get to 100 per cent charge.

Auto Express said: 'There's a little knee point where it hits constant voltage near the beginning, but does a good job of staying over 100kW for a large proportion of the time.'

Pre-conditioning EVs battery - why it's important for rapid charging

Battery pre-conditioning is when an EV battery is brought to its optimal temperature before charging, which helps it charge and perform efficiently in both hot and cold conditions. 

Auto Express said that several manufacturers have told them that the real reason their cars didn't reach the stated targets is because they didn't precondition the batteries but that this was done to create a level playing field and that some models were still able to get there meant that this should be possible across the board.

Editor Barker points out that the test is perhaps most useful for illustrating how the maximum charge rate of a car really is exactly that – a maximum – and is far from telling the whole story in terms of how quickly your car will restore power when plugged-in.