The shelf consists of a ruggedized Battery Charger, PSU with a 3-phase input for 400 / 480 VAC (line to line) and with an output suitable for 110V battery charging. DC-DC stage to convert the 3-phase input voltage to a bus voltage with battery charging capability. Emphasis is given on high reliability and long life. Two or three parallel independent units inside the shelf with active current sharing are used, which safeguards reliability and partial redundancy of the system. The PSU includes DSP which enables monitoring of electrical parameters (including input voltage of all 3 phases) and controlling the PSU from system controller. Internal RS485 / CAN bus is used for command, monitoring and diagnostic information that is supplied to the shelf controller and to the external supervising system. External communication is provided by either CAN or Ethernet communication.