A cell assembly group is provided, comprising: a plurality of cell assemblies, each cell assembly including an electrochemical cell and an outer wrap surrounding the cell; a foam sheet positioned adjacent one side of one cell assembly; a plurality of heat plates, each heat plate being positioned between two cell assemblies; and at least one spacer positioned between one heat plate and one cell assembly. Each outer wrap of each cell assembly of the plurality of cell assemblies includes a body having an inner surface that engages a rearward wall of the electrochemical cell of the cell assembly, a first portion having a flame barrier that engages a forward wall of the electrochemical cell of the cell assembly, and a second portion that engages an outer surface of the first portion.