A system comprising one or more battery modules mounted in a rack assembly has a structure which defines a cooling air pathway for flowing cooling air across the side and/or bottom of each battery module thereby cooling the battery module, or alternatively, across the energy calls in the battery module. Further, the system has a structure which defines a thermal runaway gas pathway for flowing thermal runaway gases from a battery module out of the system. The system structure is configured to ensure that the cooling air pathway and thermal runaway gas pathway are physically separated, thereby minimizing the risk of the thermal runaway gas substantially mixing with cooling air thereby potentially resulting in a spontaneous ignition and an explosion.