It is not uncommon for two independent battery circuits or two different battery types to require special mains chargers with correspondingly different charging capacities. This usually means that, in addition to the “normal” charger for the starter battery, an additional device must be installed for the special on-board battery – with all its attendant consequences: Additional costs for the device, additional effort for installation and double the space required in the vehicle. The VAC-Duo charger series, which combines two separate, independently operating chargers in one space-saving device, provides a remedy.