A rechargeable battery module is disclosed. In one aspect, the battery module includes a plurality of unit cells including first and second outermost unit cells disposed at first and second opposing ends of the unit cells arranged in a first direction, wherein the unit cells have top and bottom surfaces opposing each other. The battery module also includes a bus bar holder covering the top surface of the unit cells, a bus bar disposed at the bus bar holder to electrically connect the unit cells and a pair of end plates respectively supporting the first and second outermost unit cells. The battery module further includes a pair of side plates disposed at third and fourth opposing ends of the unit cells arranged in a second direction crossing the first direction, wherein the side plates are connected to the end plates and the bus bar holder.