Battery Pack

A battery pack comprising:

• a plurality of electrochemical cells of similar shape and size, the shape being a rectangular prism with opposing major faces, the cells being aligned in a stack along an axis of the pack so that one of the major faces of each cell contacts the major face of the adjacent cell;
• and
• a housing comprising;
• a top portion comprising a top plate and four side plates joined to the top plate so as to form a cavity with an opening, wherein the cross-sectional area of the opening is at least slightly larger than the cross-sectional area of the stack, and wherein the cross-sectional area of the cavity in a plane closer to the top plate is sized so that the stack fits snugly therein;
• and
• a bottom portion for closing the opening;
• wherein the stack is disposed in the housing;
• and
• wherein the cavity is longer along the axis at the opening and shorter at the plane closer to the top plate, to thereby press the cells against one another.