Electric UPS mixed supply system and AC-DC converter

In order to charge from a monophase alternating current voltage (Va) a battery of storage cells (10) connected to a device (61) to be supplied through an inverter (30), switching means (TA1/DA1, TA2/DA2, TB1/DB1, TB2/DB2, TC1/DC1, TC2/DC2) are used when the inverter is not in operation; said switching means are present in the inverter in order to form an alternating/direct converter (70, 71) receiving at the input a monophase alternating current voltage (Va) and delivering a direct current voltage (Vout') for charging the battery (10). According to one embodiment, the alternating-direct converter comprises a rectifier-step-up transformer stage (L1, 31, 32) followed by a step-down transformer stage (33, L2). Application particularly to electric motor vehicles.