The invention discloses a 
lithium ion battery managing 
system and an on-line measuring and diagnosing method for 
internal resistance of an electric core 
monomer. The 
lithium ion battery managing 
system comprises a main 
control unit, an electric core sensing and monitoring unit and an 
electric current sensor, and adopts a manner of high-and-
low voltage separation, wherein the electric core sensing and monitoring unit is used for monitoring and measuring the 
voltage of the electric core 
monomer of a 
lithium ion battery; the 
electric current sensor is used for measuring a 
bus electric current in a main return circuit of an electric circuit; and the main 
control unit is used for controlling the working pattern of a 
lithium ion battery set, and controlling the switching off and the switching on of a 
relay, the 
processing and the storing of data, the calculating, the 
processing and the transmitting of the 
internal resistance of the electric core 
monomer of the battery, and the diagnosing and the warning of the failure of an electric core. Through the adoption of the 
lithium ion battery managing 
system disclosed by the invention, on-line measuring of the 
internal resistance of the electric core monomer of the battery is realized, and the diagnosing of the failure and the aging of the electric core of the battery can be performed, so that the property and the condition of a 
lithium ion battery set can be more effectively monitored, effective basis is provided for the guarantee of the battery, reliable reference is provided for the exchanging of the electric core of the battery, important information is provided for the complete automobile strategy of an automobile, and the safety of the automobile, a driver and occupants are guaranteed.