In a battery (2) including a battery cell formed in a flattened substantially parallelepiped shape and a terminal contacting section (222) electrically connected to the battery cell, at one end in the longitudinal direction of a face of the battery opposing to the face on which the terminal contacting section (222) is provided, a projecting portion (26) which projects in the longitudinal direction of the face is provided. Meanwhile, another projecting portion (27) which projects in the longitudinal direction of the face is provided at the other end. The projecting portions (26, 27) may have projecting lengths different from each other or may have projecting lengths and projecting thicknesses different from each other. A charging apparatus into which the battery (2) is to be installed includes an accommodating section (40) for the battery (2) which in turn includes projection accommodating portions (46 and 47) configured to individually accommodate the projecting portions (26 and 27). The accommodating section (40) includes a space for accommodating a battery (2D, 2E) wherein the battery cell has a rectangular principal face and another space for accommodating another battery (2) wherein the battery cell has a substantially square principal face, and charging terminals serve as charging terminals not only for the battery (2) but also for the battery (2D, 2E).