Patent ID: 7852042

Claim:
A method of monitoring and controlling a voltage of at least one group of cells in a cell compound of an energy storage device in an onboard power supply system of a motor vehicle, comprising the acts of: connecting a cell group logic to the group of cells by a supply line by which the group of cells is charged or discharged; monitoring with the cell group logic the voltage of the group of cells; controlling with the cell group logic charging or discharging of the group of cells, where the cell group logic takes energy from a rail line to charge the group of cells or feeds energy to the rail line from the group of cells; conducting a data communication between the cell group logic and at least one of another cell group logic and a central logic on the rail line at voltage levels above an idle voltage level which is equal to or greater than a predetermined maximal voltage level below which the group of cells is charged or discharged; and switching the cell group logic to active when the rail line voltage is determined to be above an enable voltage level which below the predetermined maximal voltage level.