NOVELTY - Battery system comprises: (a) an external case (2) housing batteries and comprising: (i) output terminals (7); (ii) a plug connecting section (25); and (iii) receptacles (31) for insertion and connection of service plug connecting terminals; and (b) a service plug (4) that connects to the external case in a detachable manner and comprising: (i) a plug case; (ii) a fuse; and (iii) a pair of connecting terminals (51).    USE - The battery system is used in an electric powered vehicle such as an electric powered scooter or motorcycle (electric motorbike).    ADVANTAGE - The battery system has a service plug connected in a detachable manner in series with series-connected batteries.    DETAILED DESCRIPTION - Battery system comprises: (a) an external case (2) housing batteries; and (b) a service plug (4) that connects to the external case in a detachable manner. The service plug comprises: (i) a plug case that connects to the external case in a detachable manner; (ii) a fuse housed in the plug case; and (iii) a pair of connecting terminals (51) connected to the ends of the fuse. The external case comprises: (i) output terminals (7) connected to the batteries; (ii) a plug connecting section (25) for connection of the plug case; and (iii) receptacles (31) for insertion and connection of the service plug connecting terminals when the plug case is connected with the plug connecting section, where the connecting terminals electrically connect to the receptacles when the plug case of the service plug is connected with the plug connecting section; and the fuse is connected to the batteries through the connecting terminals and receptacles to output voltage across the output terminals. A gasket (49) is provided between the plug case and the plug connecting section; the service plug is connected to the external case in a water-tight configuration via the gasket; and the connecting terminals are connected to the plug case in a mechanically floating configuration that allows the connecting terminals to move perpendicular to the insertion direction.    DESCRIPTION OF DRAWING(S) - The drawing shows an exploded oblique view of the battery system.    External case (2)    Service plug (4)    Output terminals (7)    Plug connecting section (25)    Receptacles (31)    Gasket (49)    Connecting terminals (51)