In the manufacturing of battery boxes using the aluminum extruded process, poor consistency of products and a short life of the die for making aluminum structural sections are usually observed. A new method of producing battery boxes is proposed that combines steel stamped and aluminum extruded process. This paper first describes the design requirements for a battery box using a new process, and several important issues such as weld seam arrangement and error proofing in the manufacturing process are discussed. To address the issue of weld seam arrangement, the following three principles should be considered in the design: These principles include that the profile lap angle should be above 90°, three or more beams should not be lapped too closely together, and multiple brackets in close proximity should be designed as one unit. Secondly, according to the maximum external dimensions of the box and the relative position of each structure, a new box was designed in two parts: the external frame and the internal frame. In the box design, the external frame is designed from both the external frame mating surface and the external mount reinforcement, while the internal frame is solely described from the design of the internal frame mating surface. Finally, the newly designed box is subjected to finite element simulation analysis, a manufacturing process study, test verification, and bead optimization. The results show that the performance of the new battery box meets the design requirements. The study of composite process battery boxes in this paper is of guiding significance for the design of battery boxes.