The true cost of using Britain's network of public chargers to replenish the batteries of an electric car have been uncovered.

Charging an electric vehicle using a public charge point can cost almost 10 times more than charging up at home, according to research by What Car?.

It found that early adopters who regularly need to use public charging networks could save money by signing up for a scheme with a one-off or a monthly fee because these often have a lower energy usage rate.

Not as cheap as you think: Research by What Car? has uncovered the astronomical cost of charging electric cars using different public network providers

Ionity, which is a charging network as part of a joint venture between BMW Group, Daimler AG, Ford Motor Company, Hyundai Motor Group and the Volkswagen Group with Porsche AG, was found to be by far the most expensive.

It currently charges 69p per kilowatt hour of charging at its ultra rapid chargers located only at motorway services in the UK.

What Car? found that you'll pay up to an eye-watering £45.89 to charge an Audi E-tron from 10 per cent to 80 per cent at one of these devices.

Electric car owners can achieve the same level of charge using a home domestic charger at an average night-time energy tariff of 7p per kWh, which will cost just £4.66 to reach 80 per cent capacity.

What Car? said, based on these figures, that those who regularly use an expensive public chargers could end up paying more to drive their electric cars than it costs to fuel and run a comparable diesel-engined vehicle.

For instance, those using the priciest Ionity chargers to top up an E-tron's batteries will essentially be paying 34p a mile.

Owners of an Audi Q7 50 TDI diesel, which averages 27.2mpg, would - based on recent fuel prices - be paying just 22p a mile.

However, a spokesperson for Ionity said the majority of its users are those who have taken out mobility service provider (MSP) plans to use their devices.

These customers are charged a reduced tariff – similar to a phone contract – to have access to Ionity charging stations.

Ionity told us it does not have control over the costs for MSPs, but it will work out at less than the 69p kWh fee charged for one-off usage.

HOW MUCH DOES IT COST TO CHARGE AN ELECTRIC CAR USING DIFFERENT PUBLIC NETWORK PROVIDERS? Network Cost per kWh 10-80% charge Ionity (350kW) £0.69 £45.89 Polar Contactless (150kW) £0.40 £26.60 Ecotricity (22kW, 43kW, 50kW) £0.39 £25.94 Shell Recharge (50kW, 150kW) £0.39 £25.94 Instavolt (50kW to 125kW) £0.35 £23.28 Polar Instant (150kW) £0.35 £23.28 Genie Point (43kW, 50kW) £0.30 £20.95^ Polar Contactless (43kW, 50kW) £0.30 £19.95 ESV EV Solutions (43kW, 50kW) £0.29 £19.29 ESV EV Solutions (43kW, 50kW) £0.25 £16.63< Polar Instant (43kW, 50kW) £0.25 £16.63 Pod Point (43kW, 50kW) £0.23 £15.30 Charge Your Car*** (43kW, 50kW) 25p per min £13.85* Ubitricity (5.5kW) £0.20 £13.45> Polar Plus (150kW) £0.20 £13.30** Ecotricity domestic customers £0.19 £12.64 Polar Plus (43kW, 50kW) £0.15 £9.98** Source London Flexi (22kW) £0.12 £7.91*** Source London Full (22kW) £0.10 £6.32 includes £1.00 fee per charge; < £4.00 monthly fee; *kWh rates vary depending on location; > £9.99 monthly fee, plus £0.15 per charge; ** £7.85 monthly fee; ***£10.00 sign-up fee

Ionity, which is a joint venture between BMW, Daimler, Ford, Hyundai and the VW Group, was found to be the most expensive if electric car owners use its network of 350kW chargers

What Car? reviewed the costs of different public charge points based on the cost to charge the battery of an Audi E-tron from 10% to 80%

According to the latest figures from Zap Map, there are 11,007 public electric car charging locations in the UK in February 2020.

In total there are 17,767 charging devices and 30,860 individual connectors - 462 of which have been installed in the last month.

While Ionity is one of the providers with the highest charges, it is also one of a small number of extremely fast 350kW charging networks available.

Currently, the only electric car on sale capable of taking up to 200kW of charge is the new Porsche Taycan.

It means its network of rapid chargers can replenish the batteries on an average electric car on the road today in around 30 to 40 minutes, though will be future proof for the next decade.

What Ionity says... An Ionity spokesman told This is Money that it is aware that the ad-hoc charge of 69p per kilowatt hour is expensive, though there are reasons for why the price is this high. 'Ionity charging stations are only located at or near motorway services,' he explained. 'We are the only fast- charging provider that is available to all vehicle manufacturers on UK motorways, unlike Tesla's network of superchargers that are free to use but exclusively for owners of their brand of cars. 'As an infrastructure provider we have to plan ahead. Much further ahead. 'The technology we are offering - with 350kW chargers - exceeds the requirement for today's electric cars and will be good for the next 10 years. 'However, this technology comes at a cost.' Ionity originally introduced a flat rate fee of £8 to access the chargers when the first stations were installed. This was so it could 'get back end systems up and running and iron out bugs as quickly as possible'. It switched to a 69p per kWh ad-hoc fee on January 31st. 'While we admit that the 69p per kWh charge is high, the majority of our users are those who buy into mobility service provider tariffs, which charge substantially less than the 69p ad-hoc fee,' the spokesman told us. He went on to say that it is not easy or cheap to send large amounts of power to service stations, and this also has an impact on charges. 'Shorter charging times are more essential at motorways, and users do have a choice to use our chargers. 'Charging time is a factor and if you compare the charging time required by a standard public charger with 50 kW to deliver 50kWh (1 hour) compared to a 350kW charger at an Ionity station ( 10 minutes) then one could argue that is a significant benefit to the consumer. 'Those who do own electric cars tend to charge them predominantly at home - and we don't expect this to change in the future, given that the UK has some of the lowest domestic energy prices in Europe.' He added: 'It is also important to note that all our chargers source 100 per cent renewable energy, making is one of few network to do so.'

However, the study found that some slower public charging networks are also far pricier than if drivers opted to charge their plug-in cars at home.

For instance, the second most expensive is Polar Contactless. Its 150kW charge points cost £26.60 to replenish the electric Audi SUV's batteries from 10 to 80 per cent change.

And getting the same battery boost at both a 50kW Shell Recharge point and a 50kW Ecotricity socket costs £25.94, although Ecotricity rates are cheaper for its home energy customers.

As a result, What Car? recommends that regular public charger users should sign up for schemes with one-off or monthly fees, because these often have a lower energy usage rate and will result in cheaper running costs as a whole.

Sign up for a Source London Full plan, for instance, and you'll pay £4 a month, but just £6.32 every time you charge your car up.

The second most expensive is Polar Contactless - its 150kW charge points cost £26.60 to replenish the electric Audi SUV's batteries from 10 to 80 per cent change

The study found that regular public charger users could save money by signing up for a scheme with a one-off or a monthly fee because these often have a lower energy usage rate

The study also highlighted that consumers need to watch out for some hidden costs associated with the use of public chargers.

It found examples in some London car parks where electric vehicle owners are being stung £9 per hour for parking with no discount for those using on-site chargers, and What Car?'s research found overstay fees levied by charging networks to discourage that ranged from £10 to £21 per hour.

Steve Huntingford, editor of the motoring title, said: 'Although there are still a lot of slow (3kW) public charging points that are free to use, you'll have to pay if you want a quick energy fix.

'And this is where the costs can rack up if you don't research the various networks in advance.'