Electric cars: beware of unpleasant surprises when recharging

Tests by ADAC, Germany’s largest automobile club, on several models show losses ranging from 5% to almost 25%, with spectacular differences depending on the car and especially the charging method. Thus, charging from a domestic outlet is significantly less efficient, particularly due to its low power (between 2.3 and 3.7 kW).

For what? Because a battery stores direct current, while the home network provides alternating current. The conversion itself consumes energy, not counting the losses in the cables and the battery as well as the consumption of the various systems which remain active throughout the recharge. The slower the charging, the more this equipment operates and wastes energy.

ADAC compared five models under different conditions. The result is clear: the classic domestic electrical outlet is by far the least efficient solution, while the wallbox (11kW) greatly reduces losses.

It is the Mercedes CLA 350 EQ which displays the most spectacular result. Plugged into a domestic socket, it loses 24.2% of the electricity drawn. In short, almost one in four paid kilowatt hours does not end up in the battery.

The explanation lies in particular in its on-board charger: on a conventional socket, the Mercedes only draws 8 amps, compared to 10 for the other cars tested. Charging takes longer and electronic equipment therefore remains powered longer. With an 11 kW wallbox, the result changes radically: losses drop to 6.9%.

The Renault R5 E-Tech still loses 13.7% of energy when plugged into a domestic socket. But it becomes the best student in the test with an 11 kW wallbox: only 5.1% losses. In photovoltaic charging at reduced power, the figure rises to 8%.

With 12.7% losses, the Tesla Model Y obtains the best result of the five models when plugged into a domestic outlet. It nevertheless remains half as efficient as when using an 11 kW wallbox, where losses drop to 6.1%. In photovoltaic charging at reduced power, they reach 9.4%.

The Volvo EX30 loses 14.2% on a classic socket, compared to 7% on an 11 kW wallbox. Interesting feature: at 22 kW, the losses further decrease slightly, to 6.7%. This result turns the neck on a preconceived idea: reducing the charging power does not necessarily save electricity. Slower charging prolongs the operation of the vehicle’s electronic systems and can ultimately increase losses.

The Volkswagen ID.7 shows 15.3% losses on a domestic socket, the second worst result in the test behind the Mercedes. With an 11 kW wallbox, they are reduced to 6.9%. In photovoltaic charging at reduced power, they reach 10.6%.

Fast direct current (DC) charging avoids power conversion on board the vehicle, which limits losses. But then the temperature of the battery comes into play: it may need to be heated or cooled, which also uses electricity.

In another test of four models, ADAC measured overall losses of 5 to 15% fast charging. They increase in particular when a cold battery must be heated.

Above all, the ADAC advises flexible and anticipatory driving. Speed ​​is decisive: going from 100 to 120 km/h increases consumption by 26% on average. It is also better to let the car roll when possible rather than to accelerate and brake more often.

In winter, preheating the cabin while the car is still plugged in helps preserve range. Heated seats and steering wheel also consume much less energy than heating the entire cabin.

Finally, pay attention to aerodynamics: a roof box increases consumption by around 14% and a roof bike rack with two bicycles by around 33%. Correct tire pressure also helps to limit consumption.