A secondary battery module includes unit batteries arranged adjacent to each other in a battery group, the battery group having outermost surfaces. A first end-plate is disposed on one of the outermost surfaces, and a second end-plate disposed on another of the outermost surfaces. A connection rod is fixed to the first end-plate and the second end-plate through fastening members. A thickness of the first end-plate is smaller than a thickness of the first fastening member.