A battery module comprising a housing defining an internal cell cavity and cells located in the cell cavity. The housing comprises two substantially parallel walls and an end structure extending between the two walls, the end structure defining an end of the housing in a first direction, the end structure being 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 being configured such that the battery module can nest with a similar battery module.