A power supply system for an electric vehicle drivetrain includes series connected first and second high-voltage battery units, a circuit arrangement having high-power switching semiconductor devices connected to the battery units, and an electronic control system. During a charging mode, the control system controls the semiconductor devices to route high-voltage DC from a vehicle external charging source alternatingly to the battery units. During a power supply mode, the control system controls the operation of the semiconductor devices to supply high-voltage DC from both the battery units for driving a vehicle electrical traction machine of the electric vehicle drivetrain, wherein the supplied high-voltage DC has a voltage level corresponding to an accumulated voltage level of the series connected battery units.