DEGRADATION STATE DETERMINATION DEVICE AND DEGRADATION STATE DETERMINATION METHOD

A present measurement value p (k) of each of plural characteristic parameters p, representing the characteristics of a secondary battery , is input to initial characteristic model to calculate an initial characteristic estimated value p(0←k) of a first characteristic parameter as output of the initial characteristic model. A first index value F(i) representing the present state of the target is calculated based on a present time series P(i) of the measurement value p(k) of the first characteristic parameter. A second index value F(i) representing a past state of the target is calculated on the basis of a present time series P(0←k, i) of the initial characteristic estimated value p(0←k) of the first characteristic parameter. A degradation state of the target is determined based on the first index value F(i) and the second index value F(i).