NOVELTY - The device (2) has a sub-control section (222) for detecting whether or not a main control section (221) is in an abnormal condition. The sub-control section detects whether or not a high voltage battery (1) is in an abnormal condition on basis of detection data signals transmitted from a battery condition detecting section when a detection result indicates that the main control section is in the abnormal condition, and controls an electrical connection state between the battery and a vehicle driving source on basis of the detection result of the battery.    USE - Battery condition monitoring device for monitoring abnormal conditions/faults e.g. abnormal overheat conditions and abnormal overcharge conditions, of a high voltage battery e.g. rechargeable or secondary battery such as lithium battery, for supplying electric power to a vehicle driving source i.e. vehicle driving electric motor, mounted on a vehicle e.g. hybrid vehicle and electric vehicle.    ADVANTAGE - The device monitors various types of conditions of the battery for supplying the electric power to a vehicle driving system mounted on the vehicle e.g. hybrid vehicle and electric vehicle, with safe and improved malfunction resistance. The device correctly drives the vehicle driving source when the battery is in a normal operation without trouble, and can supply the electric power to the vehicle driving source even if the main control section is in the abnormal condition, thus improving and increasing fault resistance of the device. The device decreases a processing load of the sub-control section when the detection result indicates that the main control section is in the abnormal condition, thus decreasing manufacturing cost of the device.    DETAILED DESCRIPTION - The vehicle driving source is a vehicle driving electric motor (5). An INDEPENDENT CLAIM is also included for an electric power system.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of an electric power system equipped with a battery condition monitoring device.    High voltage battery (1)    Battery condition monitoring device (2)    Vehicle driving electric motor (5)    Main control section (221)    Sub-control section (222)