Electric vehicle battery pack frames constructed with extruded aluminum side and cross members. Such frames are significantly stronger than conventional cast aluminum frames, while also being much lighter than steel frames. Cross members may be affixed to side members with extruded aluminum brackets. Side members of differing lengths may be employed, to make battery pack frames of differing sizes in modular manner. Battery pack lids and bottom panels may be removably affixed to the frame such as with bolts, for improved serviceability.