Single-piece over-molded coolant subsystem

A multi-cell rechargeable energy storage system (RESS) includes a plurality of battery cells arranged in rows and a single-piece cooling subsystem configured to remove thermal energy from the plurality of battery cells. The cooling subsystem includes a cell holder constructed from an impact-resistant material defining a plurality of pockets, wherein each pocket is configured to accept and retain one of the plurality of battery cells. The cooling subsystem also includes a coolant header disposed within the cell holder and having a plurality of ribbon coolant lines arranged in parallel and configured to circulate a coolant between individual battery cells. In a cross-sectional view, each ribbon coolant line is arranged inside the cell holder and over-molded and encased by a thermal interface material (TIM). Adjacent ribbon coolant lines embrace one row of the battery cells. A method of constructing the single-piece cooling subsystem is also included.