The present invention relates to an electricity storage unit comprising a plurality of energy storage cells (1) positioned side by side and a rigid enclosure (10) surrounding said cells (1), comprising two separate parts (100A, 100B), a first part of the enclosure comprising at least one reference wall, in particular made up of a lower wall (110A), the unit comprising:—at least one stop (200, 220, 230) made from an elastically deformable material that comprises at least one so-called main wall (214, 224, 240), extending along a plane essentially normal to the reference wall (110A) and which is positioned between two of the cells (1), such that at least one stop (200, 220, 230) is placed between each pair of adjacent cells (1), and—pressing means (300) designed to bear on a face of each of the cells (1) in order to press each cell (1) against the reference wall (110A), the pressing means (300) being removably fastened to the first part (100A) of the enclosure (10).