This paper proposes a novel isolated bidirectional converter, which can efficiently transfer energy between 400 V DC micro grid and 48 V DC batteries. The proposed structure includes primary windings of two flyback transformers, which are connected in series and sharing the high DC micro grid voltage equally, and secondary windings, which are connected in parallel to batteries. Few decoupling diodes are added into the proposed circuit on both sides, which can let the leakage inductance energy of flyback transformers be recycled easily and reduce the voltage stress as well as power losses during bidirectional power transfer. Therefore, low voltage rating and low conduction resistance switches can be selected to improve system efficiency. A laboratory prototype of the proposed converter with an input/output nominal voltage of 400 V / 48 V and the maximum capacity of 500 W is implemented. The highest power conversion efficiency is 93.1 % in step-down function, and near 93 % in step-up function.