EV Charging Losses: ADAC Compares Household Outlet, Wallbox and DC Charging

© A. Krivonosov / SPEEDME

To actually put 60 kWh into the battery, a Mercedes CLA 350 EQ with ADAC-measured losses of 24.2% needs roughly 79.2 kWh from the grid. On an 11-kW wallbox, with losses of 6.9%, that drops to about 64.4 kWh. The gap approaches 15 kWh in a single charging cycle, even though the car and the battery stay exactly the same. This is SPEEDME’s calculation based on a new ADAC study.

The German automobile club compared five modern EVs, charging them between 10 and 90% with the battery starting at 20–30 °C. From a household outlet rated at 2.3 kW, losses came to 24.2% for the Mercedes CLA 350 EQ, 15.3% for the Volkswagen ID.7, 14.2% for the Volvo EX30, 13.7% for the Renault 5 E-Tech and 12.7% for the Tesla Model Y. On an 11-kW wallbox, the range narrowed to 5.1–7.0%.

The paradox comes down to time. While the car is plugged in, its control units and 12-volt electronics stay active, drawing roughly 100–300 W by ADAC’s measurements. The longer the charging session runs, the bigger the share of energy these constant loads eat up. Additional losses come from the onboard charger converting AC to DC. That means an EV’s driving consumption alone doesn’t show the full electricity bill the owner ends up paying.

The CLA turned out to be the extreme case: plugged into a household outlet, its onboard charger capped current at eight amps instead of ten, stretching the process out even further. At 11 kW, the same car’s losses fell to 6.9% — more than a third of what it lost at the outlet. The best performer on a wallbox was the Renault 5 E-Tech, at 5.1%.

Solar power changes the economics, but not the physics. Simulating PV charging at 4.1 kW, the cars lost between 8.0 and 12.8%: worse than a full wallbox, but an owner may still come out ahead accepting those losses if the power is their own and would otherwise go unused.

At fast DC stations, the conversion happens outside the car, so ADAC put the station’s own average losses at about 3%. What appears instead is the energy spent cooling or warming the battery. At 0 °C, a cold Tesla Model Y with no preconditioning lost 10% inside the car, the Renault Megane E-Tech lost 8%, the VW ID.3 lost 7% and the Hyundai Ioniq 6 lost 6%. With a warmed battery, the figures were lower. That’s exactly why conditioning the battery before a fast charge matters so much for how long you stand at the stall.

Preconditioning doesn’t create free energy, though: ADAC stresses that it simply shifts the cost from the station to the drive there. Total DC losses, counting both conversion and thermal conditioning, can run around 5–15%. So the most efficient way to charge and the cheapest one aren’t always the same thing: a public DC tariff can easily wipe out a gain of a few percentage points.

For home AC charging, the takeaway is simpler: throttling power for no reason usually isn’t worth it. The faster a compatible car and wallbox finish the job, the less time those constant auxiliary loads run — and the closer the kilowatt-hours you paid for come to the kilowatt-hours that actually land in the battery.