With the increasing electrification of vehicle power trains, the electrical energy storage unit is assuming an ever stronger role as a key technology in the drive concept. While today’s series-produced hybrid vehicles still use nickel metal- hydrid batteries, ever-greater demands are necessitating a change in technology to the lithium-ion battery. The first series-produced hybrid passenger car in Europe with the newest energy storage system is the Mercedes-Benz S 400 Hybrid. Behr describes the cooling of the battery. The supplier also presents the nature of the thermal management of battery cells in general terms to ensure full efficiency and the lifetime required.