NOVELTY - The control system (1) has a battery resistance calculating unit (7) that computes resistance estimated value which is close to one of a resistance value of a high and low resistance states. A resistance state determination unit (8) determines whether high-resistance states include resistance state of a battery (6), or exists in low resistance state. A battery control-parameter calculating unit (5) computes a control parameter of a battery system (10) to externally output using a parameter (4) for resistance estimation applicable to resistance state determination result (9).    USE - System for controlling lithium ion secondary battery of cylinder shape, flat type, square shape, coin shape, button type, and sheet type for battery system used in mobile objects such as electric vehicle such as electric-power-assisted bicycle and fuel cell electric vehicle, and hybrid vehicle such as hybrid rail vehicle and plug-in hybrid motor vehicle, for electric power storage system (all claimed) and electric power generation system. Can also be used in forklift, electric wheelchair, satellite, rocket, submarine, large sized boat and ship such as tanker, independent-power-production system, factory, house, and office.    ADVANTAGE - The high-outputting of the battery system can be enabled. The stability of the electric current and output control and reliability can be improved in the high-order control system of the battery system. The estimated precision of the battery control parameter can be improved by using the appropriate parameter for resistance estimation according to the resistance state determination result. Since the allowable electric power at the time of charge can be enlarged, the charge time is shortened, the charge efficiency can be improved and the fuel consumption of the diesel engine improved. The output of the drive system of the hybrid rail vehicle can be improved. The cost of the electric power generation system can be reduced.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic block diagram of the battery control system for the battery system. (Drawing includes non-English language text)    Lithium ion secondary battery control system (1)    Parameter for resistance estimation (4)    Battery control-parameter calculating unit (5)    Lithium ion secondary battery (6)    Battery resistance calculating unit (7)    Resistance state determination unit (8)    Resistance state determination result (9)    Battery system (10)