A battery module includes a module terminal, electrochemical cells and a bus bar that electrically connects at least a subset of the cells to the module terminal. The bus bar includes an electrically conductive substrate and an insulation layer disposed between the substrates and ends of the cells. The substrate includes primary connection through holes, each primary connection through hole having a second diameter and being aligned with the first end of a unique one of the cells. The insulation layer includes secondary connection through holes. Each secondary connection through hole has a third diameter and is concentric with a corresponding one of the primary through holes. The third diameter is less than the second diameter, and an electrical connector extends between the substrate and the cell terminal and provides an electrical connection between the substrate and the cell terminal.