In a practical embodiment, four exhaust fans were provided on the rear panel of the battery module. The corresponding heat exchanger included four gasketed apertures. The fins of the heatsink extend from the first aperture to the fourth aperture. This allows air to flow from one aperture to the next though the channels disposed between adjacent fins. The first two fans pull air from the battery module into one half of the heat exchanger. The second two fans push air from the second half of the heat exchanger into the battery module. Thus a circulatory flow is established within the battery module. The circulatory flow from the heat exchanger crosses three battery packs, three chargers, three further battery packs, and three further chargers before passing back into the heat exchanger. Internal baffling and component placement optimize air flow across the battery packs and control electronics. The battery module includes a gasket between the case and the cover to minimize hot gas leakage in the case of a thermal event.