Wallbox instead of a domestic socket: ADAC documents clear efficiency differences when charging
Anyone who charges their EV at a household socket loses a noticeable part of the energy in the process: according to a current study by the ADAC, the five electric vehicles tested each convert, depending on the model, between 10 and 30 per cent of the energy drawn from the grid into heat at the socket. You pay for that power on your bill — but it never reaches the battery.
On the measuring method
All measurements were carried out in a state-of-charge window of 10 to 90 per cent, with a starting battery temperature between 20 and 30 degrees Celsius.
Charging losses compared
The wallbox comes out clearly ahead in every class. At an 11 kW wallbox, losses ranged from 5.1 to 10.6 per cent; at a 22 kW wallbox, from 5.1 to 7.0 per cent. DC fast charging shows a range of 5 to 15 per cent — heavily dependent on battery temperature.
| Charging source | Charging power | Measured loss |
|---|---|---|
| Household socket | 2.3 kW | 10 – 30 % |
| Wallbox | 11 kW | 5.1 – 10.6 % |
| Wallbox | 22 kW | 5.1 – 7.0 % |
| DC fast charging | depending on the pillar | 5 – 15 % (temperature-dependent) |
Model comparison: who charges most efficiently
At the socket, the Mercedes CLA 350 EQ stood out with 24.2 per cent loss — the Tesla Model Y, Renault R5 E-Tech, Volvo EX30 and VW ID.7 were between 12.7 and 15.3 per cent. At the 22 kW wallbox, the field tightened considerably, between 5.1 per cent (Renault) and 6.7 per cent (Volvo EX30).
| Model | Socket (2.3 kW) | 22 kW wallbox |
|---|---|---|
| Renault R5 E-Tech | 13.7 % | 5.1 % |
| Tesla Model Y | 12.7 % | in the test field (5.1 – 6.7 %) |
| Volvo EX30 | 14.2 % | 6.7 % |
| VW ID.7 | 15.3 % | — (no 22 kW charging) |
| Mercedes CLA 350 EQ | 24.2 % (worst value) | — (no 22 kW charging) |
Why the socket performs so poorly
The ADAC named the on-board charger, auxiliary consumers in the vehicle, the charging cable and the battery itself as the main causes. At 2.3 kW charging power, a complete charging session takes accordingly long — during that time, the vehicle electronics and control units stay active and consume energy that never reaches the battery. Add to that typical line losses of up to four per cent in the home's electrical installation.
DC fast charging: efficient, but temperature-dependent
At the fast-charging pillar, household electrics and the on-board charger no longer act as losses — the ADAC pegs the conversion loss there at an average of three per cent. With an already warm battery, total losses stay low at 1 to 4 per cent. If the vehicle has to heat or cool the battery, though, they climb to 6 to 10 per cent.
For the DC measurements, the ADAC used, among others, the Hyundai Ioniq 6, Renault Megane E-Tech Electric, Tesla Model Y and VW ID.3.
Good to know: the conflict with solar surplus charging
The ADAC's rule of thumb is this: the higher the charging power, the shorter the charging session — and the lower the percentage of loss. Conversely, the popular solar surplus charging with throttled power also worsens efficiency: anyone who wants to use as much of their own solar power as possible is in a trade-off here.
Can a wallbox pay for itself?
The ADAC calculates that a wallbox can amortise itself over time — using a Renault Zoe as an example, with 10,000 km of annual mileage you save around 120 euros a year if you consistently charge at the wallbox instead of the socket.
Because charging losses stay invisible in the on-board computer, many drivers actually underestimate the energy need. The ADAC is calling on manufacturers to transparently publish charging losses in technical specifications in future.
In summary: efficiency is a question of charging power
The study's message is clear: anyone who regularly charges at home is better served in almost every respect by a wallbox — more efficient, faster and cheaper over the long term. The ADAC explicitly advises against regular charging at the household socket for safety reasons.