A battery module comprising: a housing (3a, 3b) defining an internal cell cavity; and cells located in the cell cavity; the housing comprising: a top exterior wall; a bottom exterior wall substantially parallel with the top wall; an end structure extending between the top wall and the bottom wall and between two other walls, wherein the end structure: defines an end of the housing in a first direction; is inclined with respect to the top and bottom walls such that the cell cavity extends in the first direction beyond the furthest extent of the top wall; and is configured such that the battery module can nest with a similar battery module that has been rotated about an axis transverse to the first direction with the top wall of the battery module parallel to the bottom wall of the similar battery module and the end structure of the battery module overlapping the end structure of the similar battery module in a direction perpendicular to the top wall of the battery module; and a back wall extending between and joining the top and bottom walls and the two other walls, the back wall comprising an inlet opening and an outlet opening, the said inlet opening being configured for supplying coolant to the battery module and the outlet opening being configured for draining coolant from the battery module. a housing (3a, 3b) defining an internal cell cavity; and cells located in the cell cavity; the housing comprising: a top exterior wall; a bottom exterior wall substantially parallel with the top wall; an end structure extending between the top wall and the bottom wall and between two other walls, wherein the end structure: defines an end of the housing in a first direction; is inclined with respect to the top and bottom walls such that the cell cavity extends in the first direction beyond the furthest extent of the top wall; and is configured such that the battery module can nest with a similar battery module that has been rotated about an axis transverse to the first direction with the top wall of the battery module parallel to the bottom wall of the similar battery module and the end structure of the battery module overlapping the end structure of the similar battery module in a direction perpendicular to the top wall of the battery module; and a back wall extending between and joining the top and bottom walls and the two other walls, the back wall comprising an inlet opening and an outlet opening, the said inlet opening being configured for supplying coolant to the battery module and the outlet opening being configured for draining coolant from the battery module. a top exterior wall; a bottom exterior wall substantially parallel with the top wall; an end structure extending between the top wall and the bottom wall and between two other walls, wherein the end structure: defines an end of the housing in a first direction; is inclined with respect to the top and bottom walls such that the cell cavity extends in the first direction beyond the furthest extent of the top wall; and is configured such that the battery module can nest with a similar battery module that has been rotated about an axis transverse to the first direction with the top wall of the battery module parallel to the bottom wall of the similar battery module and the end structure of the battery module overlapping the end structure of the similar battery module in a direction perpendicular to the top wall of the battery module; and defines an end of the housing in a first direction; is inclined with respect to the top and bottom walls such that the cell cavity extends in the first direction beyond the furthest extent of the top wall; and is configured such that the battery module can nest with a similar battery module that has been rotated about an axis transverse to the first direction with the top wall of the battery module parallel to the bottom wall of the similar battery module and the end structure of the battery module overlapping the end structure of the similar battery module in a direction perpendicular to the top wall of the battery module; and a back wall extending between and joining the top and bottom walls and the two other walls, the back wall comprising an inlet opening and an outlet opening, the said inlet opening being configured for supplying coolant to the battery module and the outlet opening being configured for draining coolant from the battery module.