NOVELTY - The device (100) has an assembled battery (10) connecting batteries (1) in series. An electric current bypass circuit (50) is parallelly connected with the batteries. A discharge circuit (40) carries out forced discharge of the batteries. The bypass circuit reroutes the batteries in which electricity supply is interrupted when carrying out forced discharge such that a serial connection of the assembled battery is maintained. A rectifier supplies with electricity along a discharge direction of the batteries such that the batteries connected parallelly do not short-circuit the bypass circuit.    USE - Power supply device for use in a vehicle e.g. electric vehicle such as fuel cell electric vehicle and electrically-driven motorcycle, and hybrid vehicle such as plug-in hybrid car, and electrical storage apparatus (all claimed) i.e. backup power supply apparatus, utilized for power supply applications. Uses include but are not limited to wireless base station, computer server, mobile telephone, home internal equipment, factory, street light and signal apparatus.    ADVANTAGE - The device comprises an electric current interruption mechanism that interrupts an output when abnormality of the batteries is detected such that the electric current interruption mechanism functions and connection between the batteries connected in series is partially interrupted, so that the bypass circuit reroutes the batteries in which electricity supply is interrupted when carrying out forced discharge, thus carrying out discharge easily.    DETAILED DESCRIPTION - The battery is a nickel-hydrogen battery. An INDEPENDENT CLAIM is also included for a discharge method of an assembled battery.    DESCRIPTION OF DRAWING(S) - The drawing shows a circuit block diagram of a power supply device in a state in which forced discharge of an assembled battery is carried out.'(Drawing includes non-English language text)'    Batteries (1)    Assembled battery (10)    Discharge circuit (40)    Electric current bypass circuit (50)    Power supply device (100)