Public EV charger users get just 37% of the expected rate

Charging anxiety has taken over from range anxiety as the number one reason why car buyers are shying away from switching to electric vehicles (EVs). 

In What Car? research among prospective car buyers, more than a third of the 2265 respondents who told us they were put off switching to an EV cited concerns about limitations in the UK’s public charging infrastructure. Issues with using the public charging network are the biggest barriers to EV adoption among private car buyers, among them being charging points being broken or too busy, as well as the high price of charging.

Another specific concern of car buyers is disappointing charging speeds, with complaints that the advertised charging rates at public sites are often not achievable in reality. This tallies with much of our previous experience with public chargers. 

Our latest research reveals that while some public chargers provide very swift charging, others are far slower than the advertised rates. In fact, we found that some electric car chargers are providing power at only around a third of the rates promised. 

But what are the reasons for these disappointing results, and can anything be done to resolve a situation that’s proving such a turn-off for would-be EV buyers? 

Limitations of cars

While some chargers promise power at up to 350kW, very few cars can actually accept a charge at such a high rate. All cars have a maximum charging rate; the Renault Scenic, for example, can accept up to 150kW. However, even allowing for that, there are a number of reasons why EVs might not charge at their peak rates, and it’s not all the fault of the infrastructure.

One big reason for slower than expected charging is that the vehicle restricts the amount of charge it accepts from a charger, in line with parameters determined by various conditions.

The car’s onboard systems generally allow the car to charge faster when its battery is more depleted and then slows down the rate of charge as it fills up. This is expressed by a car’s ‘charging curve’.

Charging curve data should also be available from car makers, but not all publish it and it’s not always readily available online. Looking at the charging curve will tell you roughly how quickly its battery should charge at varying states of charge.

We were able to obtain charging curve graphs from evkx.net. These enabled us to compare the rates of charge we achieved using each charger with the rates we should have received, according to the curve graph for each of our five test cars. 

Other factors that can limit a car’s charging rate include how warm the car’s battery is, the outside temperature and the age of the car and the health of its battery. 

The temperature of a car’s battery can have a big influence on charging speed and, according to many industry experts, the best way to achieve the fastest possible charge is to pre-condition the car’s battery to ensure they’re at the optimum temperature when you reach the charger. This requires the driver to set a charging station as a location on the car’s sat-nav system or to manually select pre-condition in the car’s settings.

While doing this might be simple on some vehicles, it’s not straightforward on all, and it’s not common practice among all EV drivers, especially those who use Android Auto or Apple CarPlay for navigation. 

Variables of the charging network

Even if you’re aware of your car’s charging curve and you’ve made the extra effort to pre-condition its battery, you might still not receive a public charger’s advertised charging rate. So, why is that? Well, the charging hub’s electricity supply can have a massive effect on charging rates. 

As one network manager from an unnamed nationwide charging provider explained. “Load balancing [the process of distributing power across multiple chargers] can drastically reduce charging speeds. Static load balancing means that if, for example, you have four chargers, each will receive 25%, regardless of how each is being used,” he said. So, if you have a site with four chargers and a maximum charging rate of 100kW, each charger will be able to provide only 25kW.

There is also a process called local load balancing, which varies the power according to usage. This means that if only one 150kW charger in a bank of four is being used, it’ll get 100% of the power, but if a second car plugs in, each will get 50% of the maximum output.

However, where ‘dynamic’ load balancing is employed, unused energy from elsewhere on the site can be used to boost the charging rate. 

This can work in favour of EV chargers if they are at a standalone site, but not if they’re sharing the electricity with other facilities at a particular location. In other words, EV chargers at a retail park could lose out when the shops need more power – such as at their busiest times – meaning there’s less left for the chargers. 

EV drivers have no way of knowing if any of these measures are in place at any site, and the only way they can see if they’re getting the expected charging rate is to look at the real-time kW speed on the charging unit or their car’s display screens. This is why the unnamed source said he believes that charge point operators should publish the expected charging speed at each charging site. 

A growing number of new EVs don’t state the charging speed in kilowatts on the car’s instrument panel or infotainment screen. Instead, the vehicle states the charging speed in ‘miles per hour’.

This information is useful in one way because it shows how many miles of charge you’re getting for each hour of charging. But it’s not an accurate reflection of the amount of power being pumped into the battery, because the mileage being calculated is based on the car’s official range, which is rarely achievable in real-world driving. So if your car tells you it’s getting 100 miles of charge in an hour, you’re unlikely to be able to get this range from the car if you leave the charging station and drive it along the motorway. 

What we found in real-world testing

To ensure a level playing field among our test cars, we didn’t pre-condition any of them prior to charging. Instead, we drove each test car for one and a half to two hours prior to charging. 

However, the results of our testing show that it is not essential to pre-heat batteries to gain the maximum charge. When charging our Vauxhall Astra Electric at Fastned sites in Baslidon and St Albans, we achieved the car’s top rate for its state of charge: with 31% in its battery, it charged at 100kW, and when it had 36% in its battery it achieved 83kW; these figures are in line with the charging curve for the model. 

At eight of the sites, we found that the chargers delivered power at less than two-thirds of the rate we should have received, markedly increasing the time we had to spend plugged in.

The slowest charging speed we saw was 48kW in a Renault Scenic E-Tech at an InstaVolt charger in Twickenham, Middlesex. The advertised maximum charging rate was 125kW and, although our test car was capable of charging at up to 130kW while its battery was at 4% (according to charging curve data from independent EV data website evkx.net), the fastest speed we saw of 48kW was just 37% of the expected speed. 

We also received power at 49% of the promised rate at a Shell Recharge site in Tytherington, near Macclesfield, where we charged a Peugeot e-208. The site’s maximum advertised speed was 150kW and our test car should have achieved 98kW with its batteries at 29%. However, it, too, topped out at 48kW during our charging session. 

Not all sites provided slower charging than expected, though. Two Fastned sites in Basildon, Essex, and St Albans, Hertfordshire, both provided power at 100% of the expected rate for our Vauxhall Astra Electric, and an InstaVolt charger in Bromley, Kent, gave our Vauxhall Astra Sports Tourer Electric a top speed of 98kW. 

EV public charging speeds at 15 locations

Charging point operators’ responses

We put our findings to the EV charging companies we’d visited. A Gridserve spokesperson stated: “Peak charging speeds are only available for a period of time during the charging curve. Peak charging speed and the overall speed of the charge is dependent on a number of factors including vehicle specification, state of charge, battery temperature, weather conditions and the charger you are using.

“Based on the charging sessions that we have reviewed, the charging speed was limited by the vehicle. In these situations, the charger was able to offer higher speed but the vehicle declined, choosing to charge at a lower speed.

InstaVolt CEO Delvin Lane said: “We recognise that, in some locations, grid capacity can influence the power available to chargers. Where this is the case, we optimise power distribution to ensure the best possible charging experience for all users. The Twickenham site What Car? visited has 125kW chargers operating on a dynamically shared power system, meaning power is intelligently distributed between vehicles based on demand.”

What Car? says…

Our results are a concern for all EV drivers because they highlight the fact that it’s very difficult to predict how fast a car will charge up at a public charging site. 

The number of vehicles using the charge point and the site can affect charging speed, and so can the overall amount of electricity available and how it is shared between chargers and other facilities at a site. While we understand that issues with grid capacity are being addressed by charging companies, it seems they are still an issue at some locations.

There are also a number of factors relating to the cars, including the battery management system, and external conditions, such as colder temperatures, which can slow down charging speeds. 

The bottom line is that the information provided to EV owners, from both the charging companies and car makers, needs to be improved. There should be more transparency from both about the charging speeds that are actually achievable, both from the cars at various states of charge and in different weather conditions, and from the units supplying the electricity to them and whether they are constrained in any way by the electricity supply. 

Car makers should also provide buyers with information up-front on the charging curves of their cars and other factors that could affect charging, such as pre-conditioning batteries and external temperatures. 

Some EV charge point operators show the average charging speed to the user at the end of each charge, and we think this is something that all providers should do for all locations because it gives a fairly good indication of whether or not you’ve gained your car’s optimum charging speed.

We also think the charging companies should be compelled by the Government to publish the annual average charging speeds their sites have achieved. This should be added to the requirements of the Public Charge Point Regulations, to be published alongside annual reliability data, which will become mandatory in 2026.  

These are just some of the measures we believe need to be introduced to improve the public charging experience for EV owners, and ensure motorists have a better understanding of the capabilities of their cars and the service being provided by the charging companies. They are among the issues highlighted in our EV Manifesto, which outlines the measures we believe the Government should take to encourage more people to switch to EVs. 

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