Battery Pack Box, Cell-Integrated Vehicle Body, and Electric Vehicle

A battery pack box includes a housing including a bottom shell and an enclosing frame, an upper cover, and a reinforcing structure including at least one longitudinal beam and a plurality of transverse beam brackets. The enclosing frame is fastened to the bottom shell and protrudes from the bottom shell. Each longitudinal beam is fastened to the enclosing frame in a length direction. Each transverse beam bracket is bent and protrudes away from the bottom shell and is fastened between one longitudinal beam and the enclosing frame or between any two adjacent longitudinal beams in a width direction. The upper cover is fastened on a top of the enclosing frame away from the bottom shell, and is affixed to the transverse beam brackets, serving to form at least a part of a floor of a vehicle frame.