A battery cell pack has a plurality of battery cells that are assembled into a prismatic frame, with deformable separators interposed to accommodate elastic and plastic deformation caused by cyclic and acyclic expansion and contraction thereof during charging and discharging over the life of the battery cell pack. The battery cells are arranged in a horizontal stack within the prismatic frame, and the deformable separators are interposed between subsets of the battery cells. The deformable separators exert compressive force on the subsets of the battery cells along a longitudinal axis that is defined by the horizontal stack. The compressive force exerted by the deformable separators is at least a minimum force over a service life of the battery cell pack.