A multivoltage electrical system for a motor vehicle that has a pair of storage batteries which, in a first charging mode are charged in series from the direct voltage output terminals of a bridge rectifier connected to an alternating current generator. In a second charging mode, only one of the batteries is charged and this takes place when a plurality of controlled rectifiers connecting the generator and a common junction of the batteries are gated conductive. The switching between modes is a function of the voltage of one of the batteries and the voltage of a triangular voltage waveform generator operating at a fixed frequency. The system is maintained in the second mode when generator speed is below a predetermined value.