A battery module assembly and method of assembling a battery. The battery module assembly includes a plurality of modules in which a plurality of battery cells are preassembled. The modules are compressed by end plates that are held together under compression by a plurality of linking members. The end plates may include a protrusion that applies pressure to the central portion of the battery cells within the modules. The central portion of the end plates may be partially spherical, partially cylindrical or a flat surface.