An assembled battery is formed by combining battery modules. Each battery module includes at least one battery cell and a rectangular box-shaped case that accommodates the at least one battery cell. The battery modules include a first battery module and a second battery module located adjacent to each other. The case of each of the first battery module and the second battery module includes an opposing side surface that is opposed to one of the first battery module and the second battery module. Each opposing side surface includes projections, which are laid out in rows, and ribs, which extend parallel to the layout direction of the projections. The ribs are smaller in height than the first projections. The ribs include connection ribs that connect the projections located in a predetermined range in the layout direction of the projections.