Patent ID: 8378688

Claim:
A capacity maintenance ratio determination device that determines a capacity maintenance ratio, which is a ratio of a present capacity to a reference capacity, of a chargeable and dischargeable battery based on a response signal output from said battery in response to an alternating signal having a plurality of frequency components applied from a signal generator and based on a temperature of said battery detected by a temperature detector, comprising: an impedance calculator arranged to calculate frequency characteristics of AC impedance of said battery based on said response signal output from said battery; a storage arranged to store a relationship between a value of predetermined feature information about a frequency in the frequency characteristics of the AC impedance and the capacity maintenance ratio; and a determiner arranged to determine the value of the feature information in the frequency characteristics calculated by said impedance calculator, and determine the capacity maintenance ratio corresponding to said determined value of the feature information based on the relationship stored in said storage and the temperature detected by said temperature detector.