EV drivers using public charging points are getting as little as 37% of the maximum electricity rate promised, a new study has revealed.

Chargers at eight of the sites delivered power at less than two-thirds of the rate they should have received

What Car? headed to 15 EV charging stations – operated by five different charging networks – around England and tested a variety of EVs.

The research found the chargers at eight of the sites – just over half – delivered power at less than two-thirds of the rate they should have received, markedly increasing the time the cars had to spend plugged in.

And one site provided just 37% of the charging speed the car should have been able to take.

Just three sites provided charging at the fastest possible rate.

There are a number of reasons why EVs may not charge up at the maximum stated speed, including issues with the car, the charger itself and the wider electrical infrastructure.

One commonly cited reason for slower-than-expected charging is that the vehicle restricts the amount of charge it accepts from a charger in line with parameters set by its ‘charging curve’. However, What Car? took this into account, only measuring the charge speed delivered against the rate the car should accept at any state of charge.

The poorest performance seen was at an InstaVolt charger in Twickenham, Middlesex. Here, the advertised maximum charging rate was 125kW, but while the Renault Scenic test car is capable of accepting this much electricity when its battery is at 4%, the charger actually delivered 48kW – just 37% of the figure promised.

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

Not all sites delivered 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 a Vauxhall Astra Electric hatchback. Meanwhile, an InstaVolt charger in Bromley, Kent, gave a Vauxhall Astra Sports Tourer Electric a top speed of 98kW.

What Car? Consumer editor Claire Evans said: “Our results highlight the fact that it’s almost impossible to predict how fast a car will charge up at a public charging site.

“The Government needs to make it mandatory for both the charging companies and car makers to provide EV owners with information on the charging speeds they should be getting. Charging companies should also be compelled to publish average charging speed data so EV owners can see which sites are providing charging at the expected rates.”

EV public charging speeds at 15 locations

The full study from What Car? is online here.