NOVELTY - One of the opposed surfaces of the adjacent battery cases (120) has multiple primary ribs (123A) projecting toward the other of the opposed surfaces and extending parallel to each other along one of the opposed surfaces. The other of opposed surfaces has multiple secondary ribs (123B) projecting toward the one of the opposed surfaces and extending parallel to each other along the other of the opposed surfaces. The ribs intersect each other in a cooling passage (140), and end portions of the two ribs are in contact with each other with respect to the stacking direction.    USE - Battery pack for use as power supply source for supplying electric power to object such as motor for running vehicle, and electric device.    ADVANTAGE - Since the cooling passage is the mesh-shaped continuous passage, the air flows in a weaving manner as weaving through the mesh. The air can flow in the entirety of the cooling passage in a widely spreading manner. Thus, the air can be supplied evenly and entirely over the battery cells, such that the battery cells can be effectively cooled. Since edges of the end portions of the two ribs are located in the intersectional areas, a turbulence effect of the cooling medium can be generated. Thus, boundary layers of the cooling medium are reduced in the cooling passage, and thus a heat transfer coefficient of the cooling medium is improved so that the cooling effect of the cell improves. The predetermined binding force can be evenly received throughout the two base walls and the binding force is evenly applied over the battery cells. Thus, it is less likely that a dimension of the battery cells in the stacking direction can be uneven so as to improve the battery property of the battery cells. The battery case is made of the two case units, which are joined to each other with respect to the stacking direction, so that the battery module is easily formed. Thus, manufacturing costs of the battery pack can be reduced. The battery cells are compressed evenly or overall. Thus, the evenness of the dimension of the battery cells with respect to the stacking direction improves and the battery property of the battery cells improves. Each of the ribs is not arranged to extend only in one direction, thus the stiffness difference is reduced, and thus warp of the cases can be reduced. Since the ribs are formed to have the trapezoidal cross-sectional shape, it is easy to separate a molding die from the case units after the case units are molded with a resin material. Thus, a yield ratio improves. The wall portions restrict the air from leaking from the cooling passage so as to improve the cooling efficiency of the battery cells.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of the battery pack.    Battery pack (100)    Battery case (120)    Primary rib (123A)    Secondary rib (123B)    Cooling passage (140)