Battery monitoring system and method of diagnosing the same

The invention provides a battery monitoring device and a method of diagnosing the same, which can diagnosis whether the battery state detection circuit can actuate normally or not and improve the reliability of the battery monitoring device, the battery monitoring device has each monomer voltage of a plurality of battery monomers (BC1-BC4) which are connected in series; the battery state detection circuits (270, 272, 276, 278, 400, RPU, R1-R4, RPD, MUX1-MUX5) for detecting the battery states of the battery monomers; a control circuit (30) for monitoring the states of the battery monomers according to each monomer voltage (BC1-BC4) of a plurality of battery monomers, wherein, the control circuit (30) can input analog voltage information to the battery state detection circuits (270, 272, 276, 278, 400, RPU, R1-R4, RPD, MUX1-MUX5) to diagnosis whether the battery state detection circuits can actuate normally or not.