The ADAC, in partnership with the ACL and the Danish FDM, studied the AC charging losses of five recent electric vehicles across three scenarios: a domestic socket at 2.3 kW, a wallbox at reduced power (4.1 kW), and a wallbox at maximum power (11 or 22 kW).
Charging slowly to protect the battery, or to make use of surplus power from solar panels, seems like common sense to many drivers. Yet a recent study by the ADAC, conducted with the ACL and the FDM, shows that slow charging isn’t always synonymous with energy efficiency.
The study measured electricity losses when charging five recent electric cars: the Mercedes CLA 350 EQ, Volkswagen ID.7 Tourer, Volvo EX30, Renault R5 E-Tech and Tesla Model Y. Its finding is unambiguous: the higher the charging power, the smaller the losses.
The results are especially striking for charging on a simple domestic socket. Depending on the model, between 12.7 per cent and 24.2 per cent of the energy drawn from the meter disappears before it reaches the battery. The Mercedes CLA 350 EQ shows losses of more than 24 per cent, while the Tesla Model Y fares better at 12.7 per cent. This gap is partly explained by a technical limitation: on a domestic socket, the Mercedes CLA 350 EQ can only charge at 8 A, versus 10 A for the other models tested, which extends charging time accordingly and increases the weight of fixed losses in the final tally.
Table 1 – Losses by charging mode
| Scenario | Power | Observed losses |
| Domestic socket | 2.3 kW | 12.7% to 24.2% |
| Reduced wallbox (PV) | 4.1 kW | 8.0% to 12.8% |
| Maximum wallbox | 11 to 22 kW | 5.1% to 7.0% |
Table 2 – Results by vehicle
| Vehicle | 2.3 kW | 4.1 kW | 11/22 kW |
| Mercedes CLA 350 EQ | 24.2% | 12.8% | 6.9% |
| VW ID.7 Tourer | 15.3% | 10.6% | 6.9% |
| Volvo EX30 | 14.2% | 9.1% | 7.0% (6.7% at 22 kW) |
| Renault R5 E‑Tech | 13.7% | 8.0% | 5.1% |
| Tesla Model Y | 12.7% | 9.4% | 6.1% |
The explanation is simple. Certain vehicle components draw electricity for the entire duration of the charge. The longer charging takes, the more these fixed loads weigh on the final tally. The electronic systems that convert the current also work more efficiently when operating at higher power.
Owners with solar panels can nonetheless rest easy. In the scenario simulating a charge using surplus solar power via a wallbox limited to around 4 kW, losses stay contained between 8 per cent and 12.8 per cent. The ADAC considers this level acceptable, since the electricity used is often generated directly by the household itself.
It’s nonetheless charging at maximum power that delivers the best results. At 11 kW or 22 kW depending on the vehicle, losses fall to between 5.1 per cent and 7 per cent. The Renault R5 E-Tech stands out with just 5.1 per cent losses when charging at 11 kW.
The study also debunks a common myth: having an onboard 22 kW charger doesn’t necessarily bring a dramatic gain in efficiency. The Volvo EX30, the only vehicle tested in that configuration, gains only a few tenths of a percentage point in efficiency compared with charging at 11 kW.
These results are also corroborated by independent measurements from the Green NCAP programme, which found average charging losses of 7.1 per cent across all electric vehicles tested to date, compared with an average of 6.4 per cent in the ADAC studies – a small gap that confirms the consistency of the two approaches.
The final recommendation is clear. The domestic socket should remain a back-up or emergency solution. For regular use, the wallbox is not only safer but also considerably more efficient. As for solar panel owners, they can keep favouring charging on photovoltaic surplus, even if it produces slightly higher losses.
