A micro-hybrid method and device for a motor vehicle. The device comprises, in an electrical cascade connection, a rotary electric machine, an AC-to-DC converter and a DC electrical supply bus, the DC electrical supply bus being connected to the AC-to-DC converter and being suitable for being connected to the terminals of an energy storage battery supplying an electrical distribution network of the vehicle. The device also comprises large capacity energy storage means which are mounted in parallel in relation to the cascade connection.