Electric car owners at risk of overpaying when charging

Do you want to pay more money for the same amount of electricity? No? Then you need to know your car’s maximum charging capabilities. Unfortunately, that data isn’t always handily available, meaning most EV drivers have no idea what their charging rates are.

You plug your car into a 50kW charger. It takes around 45 minutes to get the battery in your electric vehicle (EV) from 20 to 100%. This works out at around 19p per mile.

But the week after, you come across a new 350kW charger. Being seven times more powerful sounds incredibly convenient.

You eagerly plug your car in but, to your surprise, it still takes 45 minutes to charge your EV from 20-100%, except now it has cost you £37. That means you’re now paying 24.3p per mile - more expensive than your typical petrol or diesel car.

All you’ve done is pay more for the same amount of electricity.

Nothing has gone wrong here. It’s just the car in this case can draw only a maximum of 50kW DC. That means if you plug your car into a 50kW, 150kW or 350kW charger, it will only ever draw a maximum of 50kW.

Now you know this, it's unlikely you'd choose a charger that is more powerful and more expensive.

But that’s the issue. Most electric car owners do not know their car’s maximum charge rates. When we asked EV owners to name their maximum charging rates, 61% didn’t even attempt to answer, and many that did got it wrong.

We believe this is a problem that’s easily solvable by manufacturers adding the maximum AC and DC charge rates to the cars themselves. Much in the same way that when refuelling a non-electric car, the fuel flap often tells you if you need petrol or diesel.

Our independent car reviews cut through the jargon. See the best electric cars for 2022

Most common chargers: AC charging explained

Electric cars can draw power in two ways - from AC (alternating current) power supplies like the plug socket in your home (or a domestic EV charger if you have one installed), or from DC (direct current) power supplies, which you’ll only find at commercial charging stations.

As electric cars can draw from AC and DC power supplies, they have two maximum charge rates: one for AC and one for DC.

Already this sounds complicated, but the reality is that as we switch to electric cars we’re going to have to become familiar with AC and DC power, and terms like kilowatt (kW) and kilowatt-hour (kWh). These may sound like off-putting terms and conjure up unwelcome memories of O-level/GCSE physics lessons - but it can be explained simply (we promise). We explain it in greater detail in our guide on using charge points.

AC power supplies are much more common than DC. Your home’s power supply is AC, as is around 82% of the public charging infrastructure, according to statistics published by Zap Map. Here's a breakdown of the different types of AC chargers:

• Domestic three-pin plugs: 2.3 to 3kW
• Domestic EV charge points/wall chargers: typically 3.6kW or 7.2kW, occasionally 22kW
• Public ‘slow’ chargers: up to 3kW
• Public ‘fast’ chargers: 7kW-22kW
• Public ‘rapid’ AC charger: 43kW*

*Confusingly there are some 43kW AC chargers, but these are few and only some versions of the older Renault Zoe could actually make use of them. Anyone else using these 43kW plug will likely get a 7 to 11kW and potentially waste a lot of money.

Maximum AC charge rates in electric cars are typically 7kW or 11kW. When we asked EV (and plug-in hybrid, or PHEV) owners to tell us, without looking, what their maximum AC rate is, this is what they told us:

Results grouped to reduce table length

The average AC kW rate given was 23.3kW, which is more than double (in some cases triple) the amount most electric cars can draw. A minority of people said their car has 0kW AC charging, however all electric cars have AC charging capabilities.

Why is AC charging slower?

Your car’s battery, like all batteries, actually requires DC power. So when you attach an AC power supply, your car’s onboard charger converts AC to DC.

It’s this onboard charger that limits the power your car can receive, most output 7kW or 11kW. Very few cars have 22kW capability, though it is slowly becoming more common with cars like the Audi e-tron GT (2021-) and new Nissan Ariya (2022-) offering 22kW AC capability as an optional extra (in other words, you have to pay more for it when ordering the car).

It's important to stress that there’s no safety issue here. You can attach a 22kW charger to a car that has a maximum AC capability of 7kW and the car will draw only a maximum of 7kW. You're not going to damage your car by plugging it into a faster charger.

However, the issue is that if you don’t know the maximum AC rate of charge your electric car can take, you might end up choosing a charger with a higher rate of power when it’s of no use to you.

That could take the charger away from another electric car driver that can use it. The more powerful the charger, the more you are likely to pay for it, but this is more prevalent in DC charging.

Quickest charging: DC charging explained

If you attach a DC supply to your electric car, it will not need to be converted like AC does, and so you can provide much quicker charging.

Types of DC charger:

• Rapid chargers: Typically 50kW, but technically anything between 25kW and 99kW
• Ultra rapid chargers: 100kW and above. 350kW is the current maximum in the UK, though Shell has recently unveiled a 360kW charger.

Most electric cars have a DC charge rate somewhere between 50-150kW, though there are a select few, such as the Hyundai Ioniq 5 (2021-) and Porsche Taycan (2020-) that can draw more than 200kW. Naturally the more your car can draw, the faster it will charge.

No car available can yet draw 350kW. There are a number of 350kW chargers in the UK and it is expected that EVs will be able to make fuller use of them in the future.

DC chargers will typically charge you much more than AC chargers. Our research shows that even with fuel prices as high as they are, the more expensive DC chargers cost more than equivalent petrol and diesel cars.

But our survey of EV and PHEV owners shows a number of misunderstandings. Of the 39% of drivers that provided their DC charge rates:

• Nearly a third (32%) of drivers listed their DC charge rate of 22kW or lower, when typically DC charging starts at 50kW
• Whereas 20% of drivers said their car’s AC charging was higher than its DC charging
• 3% of EV owners listed a DC capability of 350kW.
• A few drivers listed their maximum AC charging at 340-350kW.

Which? calling for clarity

Which? car researcher Adrian Porter said ‘Our survey is a clear indicator that most have no idea what charger their cars are best suited to.

‘The more powerful the charger, the more costly it tends to be. There is absolutely nothing wrong with future proofing and providing ultra-high power chargers, but consumers need to be aware of what power their car is capable of receiving.

‘Again, it’s fine if people want to pay high rates - and they may have little choice depending on charger provision where they are -  but they should do so knowingly.

‘There’s a lot of new information that EV drivers need to learn, so it’s completely reasonable that people are currently unaware of their charging rates.

‘More education at the point of sale would be welcome, but we think the most effective way to make this simpler is to put the maximum AC and DC charge rates to the sockets on the car’s themselves. So that’s what we’re calling on car manufacturers to do.’

There are further complications - like the fact when charging from a DC power supply, you’re only going to get the maximum power until your battery is 30% full. Then it decreases as the battery fills further, and slows a lot when it hits 80% to preserve the health of the battery.

Our guides on charging an electric car explain everything from how long it takes to charge an electric car (and why electricity can be more expensive than diesel), to charging at home and using the public charging infrastructure. 

We’re working to make EV life simpler, from adding AC and DC charge rates to cars, to making payments easier and improving charge point reliability. Read more about our vision for an EV future by heading to our paper on Building an Electric Vehicle Charging Infrastructure that is Fit for the Future.

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