The internal volume of the battery module and heat exchanger are sealed to each other with a gasket 58. This internal fixed volume requires pressure venting in the case of a thermal event to avoid the build up of explosive pressure. Accordingly, the heat exchanger is provided with a duct that communicates from the sealed internal volume to an external vent via piping. The piping may be provided with a check valve to prevent warm external air from entering the heat exchanger or plenum. The heat exchanger includes an overpressure relief port 46 to duct hot gas venting in the case of a thermal event. Relief port 46 is in communication with an exhaust manifold 54 disposed behind the cold plate 50. Within the internal volume, there is also provided a desiccant for moisture control. The panels in combination with the housing are designed to channel any hot gases and direct them along the air flow circulatory path out the back of the battery module into the heat exchanger where they can be exhausted through the vent. In summary, heat management is provided by the insulating material encasing the cells in addition to baffles and housing configuration designed to direct air flow through the heat exchanger.