A method of mounting a battery box (10) on a frame rail (12). Fasteners and elements (36, 38; or 54, 56) provide spaced apart, axially tapered outer surfaces (46; 62) proximate a vertical side of the rail with the tapers narrowing toward the side of the rail. The box has tabs (28) having downwardly open throats (30). The box is hung on the rail by positioning the box so as to place each tab over a respective element (38 or 56) on the fastener (36 or 54) with the tab throat aligned with the element, and then lowering the box to cause the elements to enter the tab throats and the throats to come to rest on the elements so that at least some of the weight of the box is borne by the rail through the throats resting on the elements. With the throats resting on the elements, the tapered outer surfaces present axial interference to the tabs beyond the tabs relative to the rail. After the box has been hung, the box is fastened to the rail by additional fasteners.