NOVELTY - Battery pack that can be attached to electric equipment to be supplied with electric power and can be attached to a charger for charging the battery pack, comprises: (a) rechargeable batteries (39) for supplying electric power; (b) a battery holder (70) that holds the rechargeable batteries; (c) a pack circuit board (74); (d) a casing that accommodates the battery holder and the pack circuit board; (e) external connection terminals (33) that are fastened onto the pack circuit board and are connected to the rechargeable batteries; and (f) a lock hook that holds the battery pack.    USE - The battery pack is used for supplying electric power to the electric equipment. It can be used as electric tool battery pack, and battery packs for mobile devices such as power-assisted bicycle, electric motorcycle, and mobile phone.    ADVANTAGE - The battery pack has improved waterproof structure.    DETAILED DESCRIPTION - Battery pack that can be attached to electric equipment to be supplied with electric power and can be attached to a charger for charging the battery pack, comprises: (a) rechargeable batteries (39) for supplying electric power to the electric equipment; (b) a battery holder (70) that holds the rechargeable batteries; (c) a pack circuit board (74) that includes an electronic circuit connected to the rechargeable batteries; (d) a casing that accommodates the battery holder and the pack circuit board; (e) external connection terminals (33) that are fastened onto the pack circuit board and are connected to the rechargeable batteries, where the external connection terminals are exposed externally of the casing; and (f) a lock hook that protrudes from a surface of the casing, and holds the battery pack with the battery pack being attached to the charger and/or the electric equipment. A hook opening window is opened in one of the surfaces of the casing so that the lock hook can protrude from the surface of the casing, a partition rib extends inside the casing along the hook opening window for the lock hook, and the edge of the partition rib contacts the pack circuit board.    DESCRIPTION OF DRAWING(S) - The drawing shows a perspective view of a battery pack.    External connection terminals (33)    Rechargeable batteries (39)    Battery holder (70)    Pack circuit board (74)    Inclined surface (78)    Gateway (79)