NOVELTY - The battery cell (100) has an electrode assembly (110) inserted into electrolyte. A case (120) accommodates the electrode assembly that is transformed according to shape of a specific device. A wrinkle preventing unit i.e. sheet-type unit, is located at an inner surface of the case. The wrinkle preventing unit prevents wrinkle of outermost electrodes that are arranged on the electrode assembly. A separation film (113) is located between an anode (112) and a cathode (114). The wrinkle preventing unit is formed with multiple pores. Diameter of one of the pores is 0.1-1 mm.    USE - Battery cell e.g. pouch-type battery cell, lithium secondary battery cell and lithium ion secondary battery cell, for use in a battery pack of a power source device of an electronic device e.g. handheld computer, smart phone, hand frit PC, smart pad and netbook, a vehicle e.g. electric vehicle, hybrid electric vehicle, plug-in hybrid electric vehicle and light electronic vehicle (LEV), and a power storage system (all claimed).    ADVANTAGE - The wrinkle preventing unit prevents the wrinkle of the outermost electrodes that are arranged on the electrode assembly so as to effectively prevent deformation of the battery cell due to exposure or electrolyte leakage phenomenon occurrence, so that safety of the battery cell can be enhanced and energy density and output stabilization effect of the battery cell can be improved.    DETAILED DESCRIPTION - The wrinkle preventing unit is made of insulating material, metal material or membranous polymers material that is polyethylene, polypropylene, polystyrene, PET, polymethylmethacrylate, polyacrylonitrile, silicone resin or natural/synthetic rubber material. The insulating material is polyolefin resin, fluorine resin, silicone resin or the gum-resin. The metal material is aluminum, copper, iron or nickel. An INDEPENDENT CLAIM is also included for a power source device.    DESCRIPTION OF DRAWING(S) - The drawing shows a partially enlarged cross-sectional view of a battery cell.    Battery cell (100)    Electrode assembly (110)    Anode (112)    Separation film (113)    Cathode (114)    Case (120)