Battery pack having cooling system

A battery pack having a cooling system, comprising:

• a plurality of battery units linked in series or in parallel and arranged in a plane for providing power;
• a plurality of thermal conducting bars each has at least four lateral faces and two ends, averagely located among the battery units and substantially contacted to the battery units by the lateral faces, for conducting heat out of the battery units to the two ends;
• and
• a housing for containing the battery units and thermal conducting bars and conducting heat from the ends of the thermal conducting bars to outside of the housing;
• wherein each lateral face has a same area and shape;
• and
• wherein at least one end of the thermal conducting bar is connected to the housing and becomes an internal supporting structure of the housing.