An emergency lighting unit for supplying emergency lighting unit, comprising mains supply terminals, at least one first battery module comprising one or more cells in parallel, at least one second battery module comprising one or more cells and being connected in parallel to the at least one first battery module, a preferably common charging circuit for the first and second battery module and connected to the mains supply terminals, and an emergency driver circuit for supplying the emergency lighting unit off terminals of the emergency lighting unit, wherein the charging circuit is configured to charge and maintain the at least one second battery module to a charging voltage of maximum 50%, preferably maximum 30%, of a nominal charging voltage of the at least first battery module.