Abstract: A packaging process for slim batteries includes providing a first board. The surrounding edge of the first board extends to form a plurality of first jointing flakes. A frame is formed by an insert molding method and combined with the first board. There is a plurality of jointing slots on the side walls of the frame. The first jointing flakes are embedded into the side walls of the frame to fasten the first board onto the bottom of the frame. A battery module is provided. The battery module is placed into the frame, and the battery module is located on the first board. A second board is provided. The surrounding edge of the second board extends to form a plurality of second jointing flakes. The second jointing flakes are combined with the jointing slots by ultrasonic to fasten the second board onto the top of the frame.