The invention relates to a power storage module (10) capable of containing a plurality of power storage elements (14), the module including: a housing (16) including at least a plurality of side walls and two end walls (18A; 18B), the side walls consisting of one piece (20) having a closed outline and being sized so as to surround the power storage elements; a wall (22) for supporting the power storage elements, which is separate from the walls of the housing, and which extends essentially parallel to one of the side walls, referred to as a reference wall (20A); a means (24A-24B) for changing the position of the supporting wall (22) between at least an assembly position, in which the supporting wall is located at a first distance from the reference wall (20A), and an operating position, in which the supporting wall is located at a second distance from the reference wall (20A) that is greater than the first distance.