A bicycle electronic system comprising a battery unit, at least one operating unit and a power supply and communication bus, each of said units being connected to said bus is provided. The system comprises first means or controller for switching-off/(re)switching-on able to be activated/deactivated by a user and second means or controller for switching-off/(re)switching-on suitable for disconnecting/connecting said battery unit from/to said power supply and communication bus in response to the activation/deactivation of said first means or controller for switching-off/(re)switching-on. A battery unit and a method for switching-off/(re)switching-on a bicycle electronic system are also described.