A master electronic control unit controls a plurality of batteries, and is communicatively connected to each one of the battery control units. The master electronic control unit provides a predefined electric interference to the traction voltage bus after a signal to open the at least one contactor of each battery has been provided. Each battery control unit detects the predefined electric interference, and when the predefined electric interference is detected, the at least one battery control unit issues a signal that the predefined electric interference was detected.