An apparatus (101, 101B, 101C, 101D, 101E), an electrical system (706), a vehicle (701) and a method (800) are disclosed. The apparatus (101) comprises a plurality of battery cells (102), each of the battery cells (102) comprising a layer of positive electrode material (103), a layer of electrolyte material (104) and a layer of negative electrode material (105). The apparatus also comprises a container means for containing battery cells (106, 106B, 106D, 6E) formed of an electrically conductive material and having a plurality of cavities (107). Each of the cavities contains at least a respective one of the battery cells (102), and the container means (106, 106B, 106D, 106E) is in direct contact with at least one of the positive electrode material (103) and the electrolyte material (104) of each battery cell (102) or alternatively at least one of the negative electrode material (105) and the electrolyte material (104) of each battery cell (102).