The passive environmental management module includes a heat sink having a plurality of cooling fins arranged parallel to a fin axis. The cooling fans include an inflow cooling fan that draws air from the passive environmental management module through one of the ducts into the active module. The outflow cooling fan that draws air from said active module through the other one of the ducts into said passive environmental management module. The cooling fans circulate air through the cooling fins along the fin axis in a direction from the outflow cooling fan to the inflow cooling fan that is orthogonal to the stack axis. The cooling fans circulate air between the active module and the passive environmental management module in a loop encompassing a circulating plane that includes the fin axis and is orthogonal to the stack axis.

The passive environmental management module includes an overpressure relief port that vents heat and smoke from a faulty battery cell out of the housing in a vent direction that is orthogonal to the stack axis and is orthogonal to the fin axis. The active module includes insulation made from intumescent material surrounding said battery cells to absorb heat from a faulty battery cell. A group of battery cells are contained with an upper and a lower end cap that are arranged on the battery cells along the stack axis to prevent an explosive thermal event from damaging an adjacent cartridge. The housing is oriented so that the overpressure relief port is at the top of the passive environmental management module.