A battery pack comprising: - a housing and an upper cover, wherein the housing has a bottom portion, a first length side wall, a second length side wall, a first width side wall and a second width side wall that extend upward surrounding a periphery of the bottom portion; the first length side wall, the second length side wall, the first width side wall and the second width side wall form an upper portion opening; the upper cover is mounted on the upper portion opening of the housing; - multiple flat battery cells sequentially arranged and mounted in the housing; - a bearing plate disposed above top portions of the multiple battery cells; - a middle recessed portion formed between protruding battery cell anode and battery cell cathode disposed on the top portion of each of the multiple battery cells; and - a first end plate and a second end plate, wherein when the multiple battery cells are sequentially arranged and mounted into the housing, the first end plate and the second end plate are located at two end sides of the sequentially arranged multiple battery cells to laterally fix the sequentially arranged multiple battery cells, wherein a surface of the middle recessed portion is provided with at least one seal-breakable opening configured to discharge a gas generated in the battery cell when broken; wherein the multiple middle recessed portions at the top portions of the multiple battery cells form a battery top portion through-slot when the multiple battery cells are sequentially arranged and mounted in the housing; wherein a bottom portion of the bearing plate is provided with a bearing plate bottom portion through-slot, and when the bearing plate is mounted above the top portions of the multiple battery cells, the bearing plate bottom portion through-slot is press-fitted with the battery top portion through-slot to form a lateral gas discharging passage, wherein one end of the lateral gas discharging passage is provided with an outlet, and another end of the lateral gas discharging passage is blocked; wherein the housing comprises a vertical gas discharging passage, and the vertical gas discharging passage is disposed on an inner side of the first width side wall, and the first width side wall is provided with a gas discharging port; and the vertical gas discharging passage is in fluid communication with the lateral gas discharging passage; and wherein an upper end of the first end plate is provided with a ventilation guide slot, and the ventilation guide slot is located between the lateral gas discharging passage and the vertical gas discharging passage to enable the lateral gas discharging passage to be in fluid communication with the vertical gas discharging passage. - a housing and an upper cover, wherein the housing has a bottom portion, a first length side wall, a second length side wall, a first width side wall and a second width side wall that extend upward surrounding a periphery of the bottom portion; the first length side wall, the second length side wall, the first width side wall and the second width side wall form an upper portion opening; the upper cover is mounted on the upper portion opening of the housing; - multiple flat battery cells sequentially arranged and mounted in the housing; - a bearing plate disposed above top portions of the multiple battery cells; - a middle recessed portion formed between protruding battery cell anode and battery cell cathode disposed on the top portion of each of the multiple battery cells; and - a first end plate and a second end plate, wherein when the multiple battery cells are sequentially arranged and mounted into the housing, the first end plate and the second end plate are located at two end sides of the sequentially arranged multiple battery cells to laterally fix the sequentially arranged multiple battery cells, wherein a surface of the middle recessed portion is provided with at least one seal-breakable opening configured to discharge a gas generated in the battery cell when broken; wherein the multiple middle recessed portions at the top portions of the multiple battery cells form a battery top portion through-slot when the multiple battery cells are sequentially arranged and mounted in the housing; wherein a bottom portion of the bearing plate is provided with a bearing plate bottom portion through-slot, and when the bearing plate is mounted above the top portions of the multiple battery cells, the bearing plate bottom portion through-slot is press-fitted with the battery top portion through-slot to form a lateral gas discharging passage, wherein one end of the lateral gas discharging passage is provided with an outlet, and another end of the lateral gas discharging passage is blocked; wherein the housing comprises a vertical gas discharging passage, and the vertical gas discharging passage is disposed on an inner side of the first width side wall, and the first width side wall is provided with a gas discharging port; and the vertical gas discharging passage is in fluid communication with the lateral gas discharging passage; and wherein an upper end of the first end plate is provided with a ventilation guide slot, and the ventilation guide slot is located between the lateral gas discharging passage and the vertical gas discharging passage to enable the lateral gas discharging passage to be in fluid communication with the vertical gas discharging passage.