A battery or fuel cell module comprising a plurality of battery cells or fuel cells and metal foam bus bars that electrically connect together at least some of the battery cells or fuel cells is described. The battery or fuel cell module may further include a cooling system arranged to provide a flow of cooling fluid through the metal foam bus bars to remove heat from the bus bars. In some examples, the cooling system comprises one or more forced air devices. In other examples, the metal foam bus bars are encased in a fluid-impermeable skin so that the bus bars form fluid-tight pipes with a metal foam interior, and the cooling system is arranged to provide the flow of cooling fluid through the metal foam interior of the fluid-tight pipes.