TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Component: Each terminal has a planar shape. The upper sheath member includes a corner portion having a part vertical to the flat wall. The corner portion is molded in a position corresponding to a corner of the power-generating element. The positive and negative plates contain positive and negative electrode active material, respectively. Each flat cell is stacked on another flat cell with the positive terminal directed in the same direction as the positive terminal of another flat cell. The terminals with same polarities of the flat cell and another flat cell are connected to each other to form the battery. Preferred Condition: Before an inside of the cell is evacuated, the inclined wall is inclined at 45-80degrees with respect to the surfaces of the terminals. Before an inside of the cell is evacuated, the inclined wall is molded in parallel to a collector positioned closest to the member among the collectors. Before an inside of the cell is evacuated, the inclined wall is curved toward the inside of the cell. Preferred Parameter: The length of the vertical part included in the corner portion is larger than the total thickness of the positive plate, the negative plate, and the separator.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Material: The positive terminal contains aluminum, iron, copper, and/or nickel. The positive electrode active material is a lithium-based composite oxide, preferably lithium-manganese-based composite oxide. The negative electrode active material is a carbon material, preferably crystalline carbon material or amorphous carbon material.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Material: The positive terminal contains aluminum, iron, copper, and/or nickel. The positive electrode active material is a lithium-based composite oxide, preferably lithium-manganese-based composite oxide. The negative electrode active material is a carbon material, preferably crystalline carbon material or amorphous carbon material.    TECHNOLOGY FOCUS - POLYMERS - Preferred Material: The sheath member contains polypropylene, modified polypropylene, polyethylene, modified polyethylene, and/or ionomer.