The invention concerns a device for managing power supply of a motor vehicle multimedia system, comprising a number of modules each having at least one function requiring electrical power supply, in particular in standby mode, such that it consists of a module receiving in input: a permanent electrical power supply from the vehicle battery; wake-up/sleep data from the vehicle control computer, based on the contact key in particular and from control means particular to the multimedia system; optionally wake-up and/or sleep control signals from certain modules belonging to the multimedia system itself, for: delivering to said multimedia system modules wake-up/sleep and/or switched power supply signals; saving data in the volatile storage means; keeping time through the metering means.