PROBLEM TO BE SOLVED: To predict a remaining life of the storage battery with a high accuracy.SOLUTION: A storage battery deterioration diagnostic method includes the steps of: finding a SOC-OCV curve showing a relation between a storage battery residual amount SOC of a storage battery and an open-circuit voltage OCV; identifying the OCV by applying an inter-terminal voltage uof the storage battery and a discharge current i to an equivalent circuit model 20; estimating the SOC using the OCV and the SOC-OCV curve; estimating a battery capacity using the SOC; and predicting a remaining life on the basis of the battery capacity. In identifying the OCV, internal impedances Ra, Rb, and Cb are identified using a predetermined identification expression derived from the equivalent circuit model 20 of the storage battery with the OCV derived as fixed, and the OCV is identified by applying the identified internal impedances Ra, Rb, and Cb to the predetermined identification expression. Thereby, the battery capacity of the storage battery can be estimated with a high accuracy, and the estimation accuracy of the SOC and the battery capacity of the storage battery can be increased, and the remaining life of the storage battery can be predicted with a high accuracy.SELECTED DRAWING: Figure 2
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