EV charging losses and heat‑related battery aging revealed in studies

A study by the German ADAC examined charging losses in five current electric‑vehicle models when charged from a household socket versus a wallbox. Charging at a 2.3 kW household outlet produced the highest losses, with the Mercedes‑Benz CLA EQ losing almost a quarter of the supplied electricity and the other models around 15 %. Using a wallbox at the vehicle’s maximum power (11 kW or 22 kW) reduced losses to under 7 %, with the Renault R 5 showing the lowest losses in both wallbox and solar‑surplus charging scenarios. The ADAC concluded that household sockets are unsuitable for regular EV charging and should be used only as a backup.

Separate research highlighted the impact of summer heat on EV batteries. A 2014 RWTH Aachen study and a 2025 Stanford Linear Accelerator Center investigation found that high ambient temperatures combined with a high state of charge accelerate lithium‑ion cell aging, increasing capacity loss and internal resistance. The effect varies by cell chemistry, and a fully charged battery is not inherently damaging if exposure to heat is brief. Drivers are advised to avoid leaving fully charged EVs in hot conditions for extended periods.