Method for detecting state of secondary battery and device for detecting state of second battery

A device for detecting the state of a secondary battery, comprising:

• a current measurement portion that measures the current flowing through the secondary battery as current data;
• a voltage measurement portion that measures the terminal voltage of the secondary battery as voltage data;
• a data set selection portion that acquires a plurality of data sets comprising the current data from the current measurement portion and the voltage data from the voltage measurement portion that corresponds to the current data, and that outputs the plurality of data sets as valid data sets when specific selection conditions are satisfied;
• an internal-resistance-during-charging-and-discharging calculation portion that performs statistical processing with respect to the plurality of valid data sets during charging and discharging, and calculating a value of internal resistance during charging and discharging of the secondary battery from the slope of a linear approximation obtained by the statistical processing;
• an internal-resistance-during-charging calculation portion that performs statistical processing with respect to the plurality of valid data sets during charging, and calculating a value of internal resistance during charging of the secondary battery from the slope of a linear approximation obtained by the statistical processing;
• a difference computation portion that calculates an absolute value of the difference between the value of internal resistance during charging and discharging and the value of internal resistance during charging, and that also outputs a signal indicating the magnitude correlation between the value of internal resistance during charging and discharging and the value of internal resistance during charging;
• and
• a judgment portion that judges whether or not the absolute value of the difference from the difference computation portion is equal to or less than a first predetermined value, and that outputs the value of internal resistance during charging and discharging or the value of internal resistance during charging, whichever is smaller, as a value of internal resistance of the secondary battery when the absolute value of the difference is equal to or less than the first predetermined value.