Abstract: A modular battery pack assembly and method of making the same. Prismatic battery cells are placed along a stacking axis within a structural frame that is made of a polymeric material that includes foldable components made up of a top section disposed adjacent an edge of the stacked cells, and numerous side sections cooperatively coupled to the top sections to define an enclosure about the cells. In one form, apertures, protrusions and other features may be formed in or on the enclosure surface that faces or otherwise engages the cells, while in another form, built-in hinges permit selective latching between adjacent enclosure sections. A bottom section, which may be made of the same or similar material, may be secured to the remainder of the enclosure that is formed by the top and side sections such that the stacked cells are completely enclosed in a portable, modular assembly.