Abstract: A modular backup power housing consists of at least one module and a base. Additional modules may be stacked to accommodate a larger bank of power cells. Each module has a cuboid frame, multiple top rails and multiple bottom tracks. The top rails and the bottom tracks are attached to top and bottom surfaces of the cuboid frame respectively and mate with the top rails and bottom tracks of adjacent modules or the base. By virtue of the interlocking top rails and bottom tracks, the total height of the modular backup power housing is less than a conventional housing, and the strength and stability of the modular backup power housing is improved.