NOVELTY - The battery pack (800) has a rear surface mounting portion (500) whose end portions (502,504) are connected with exterior device. Battery cells are arranged above a lower support portion (740). Battery modules (602,604) are laminated and combined with the lower portions of a front side supporting portion (400) and a backside support portion (410). A weak point (401) that is prone to volumetric expansion is partially provided on pair of side support portions to induce localized deformation of the battery module when swelling occurs so that power supply is suspended.    USE - Battery pack mounted between rear seats of trunk of vehicle such as hybrid electric vehicle, plug-in hybrid electric vehicle and electric vehicle (all claimed) e.g. electric bicycle, for providing power. Can also be used in cellular phone, digital camera, personal digital assistant, portable media player and notebook computer.    ADVANTAGE - Since weak point that is prone to volumetric expansion is partially provided on pair of side support portions to induce localized deformation of the battery module when swelling occurs so that power supply is suspended, the electrical contact of the outermost battery module is cut and the rechargeable procedure is stopped. The swelling volume of the battery pack can be suppressed. The abnormal operation of the battery pack or long-term charging/discharging of the battery pack can be prevented. Hence firing and explosion of the battery pack can be prevented and safety of the battery pack can be ensured. The deformation of upper fitting area and rear surface mounting portion can be prevented. The side support portions can improve the unity force between the battery modules. The structure of the battery pack can be maintained in the environment such as impact and vibration. The pair of side support portions authentically can reinforce the bending stiffness of lower support portion bonded to the lower portion of the side support portions and front side and rear surface of the battery module array are supported. The structural shin lightning province of the battery pack can be secured. The performance degradation of the battery pack can be prevented. Since the battery module is comprised of battery management system and shutting structure, the malfunction of battery management system can be prevented and safety can be ensured even when battery management system is not operated. The reliability and durability of the battery pack can be improved. Heat generation by the battery pack can be reduced. The generation of vibration from the battery pack can be prevented. The space occupied by the battery pack in the vehicle can be reduced. Compact battery pack can be obtained.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of the battery pack.    Front side supporting portion (400)    Weak point (401)    Backside support portion (410)    Rear surface mounting portion (500)    End portions (502,504)    Battery modules (602,604)    Lower support portion (740)    Battery pack (800)