The first exterior wall 28 includes at least one duct 26 in the upper half for an inflow cooling fan and at least one duct 26 in the lower half for an outflow cooling fan. The inflow cooling fan 60a rotates about an inflow cooling fan axis 60b that extends between two battery packs. If three battery packs are present, two inflow cooling fans would be provided to introduce cooling air into the space between two adjacent battery packs, respectively. The outflow cooling fan 60c rotates about an inflow cooling fan axis 60d that extends between two battery packs. If three battery packs are present, two outflow cooling fans would be provided to draw cooling air from the space between two adjacent battery packs, respectively. A baffle 22f extends from the back wall 28b toward first exterior wall 28. The baffle is spaced from first exterior wall 28 thereby providing a gap 22r. An optional supplemental fan 22s may be disposed in the gap 22r. The baffle divides the interior space 22g into a first interior space portion 22h and a second interior space portion 22i. The inflow cooling fan introduces cooling air into the first interior space portion 22h. The cooling air then flow along the first exterior wall 28. The cooling air is then drawn out by outflow cooling fan through second interior space portion 22i. The cooling air is then circulated from bottom to top through passive environmental management module 40. The cooling air thus flow around a loop 62 through ducts 26 within a sealed internal space comprising the active battery module 20 and the passive environmental management module 40. The loop 62 includes a circulating plane 62a that is parallel to housing lid 14b (FIG. 3). Circulating plane 62a is co-planar to fin axis 44y and vent direction 46z. Circulating plane 62a is orthogonal to stack axis 12x.