NOVELTY - The battery pack has a main body formed with an internal space. An outer side protrusion part (110) is fixed between top and bottom parts of an outer profile in a cell assembly (100). The cell assembly is provided with the pack housing. An inner side protrusion part (210) is arranged between top and bottom parts of an inner side wall in the pack housing. A sensing assembly (300) is equipped in a side of the cell assembly. The outer side protrusion part and the inner side protrusion part are jointed with each other. A duct is fixed on a mounting portion (220) of the pack housing.    USE - Battery pack for a secondary battery in a vehicle (claimed) e.g. car, such as electric vehicle and hybrid electric vehicle, and a portable appliance e.g. notebook, video camera and pocket telephone. Uses include but are not limited to nickel cadmium battery, nickel-hydrogen electric cell, nickel zinc cell and lithium secondary battery.    ADVANTAGE - The battery pack improves rigidity of the cell assembly and the pack housing. The battery pack prevents generation of external shock or vibration, so that the cell assembly or pack housing is prevented from being damaged. The battery pack avoids occurrence of external vibration or impact, so that convenient usage of the battery pack can be improved. The battery pack simplifies assembling process of the pack housing and the cell assembly. The battery pack can adjust retracted position of the pack housing and the cell assembly in an automatic manner, so that the battery pack can be accurately fitted on the retracted position, thus reducing assembling cost of the battery pack. The battery pack avoids danger of eutectic phase difficulty or generation of damage during moving process of the cell assembly.    DESCRIPTION OF DRAWING(S) - The drawing shows an exploded perspective view of a battery pack.    Cell assembly (100)    Outer side protrusion part (110)    Inner side protrusion part (210)    Mounting portion (220)    Sensing assembly (300)