Battery state estimating apparatus

A battery state estimating apparatus comprising:

• an acquirer configured to obtain a plurality of complex impedances of a battery at a plurality of different temperatures;
• a calculator configured to calculate a slope of a first straight line or a slope of a second straight line as an impedance slope on a complex plane having an axis that is a real component of the complex impedance and an axis that is an imaginary component of the complex impedance, wherein the first straight line connects values of the obtained plurality of complex impedances at a first predetermined frequency, wherein the second straight line connects a convergence point and at least one of values of the plurality of complex impedances at a second predetermined frequency, wherein the convergence point is a point on which intersections of straight lines and the axis that is the real component converge when the second predetermined frequency is changed, and wherein each of the straight lines connects the values of the complex impedances at the second predetermined frequency;
• a determinator configured to determine whether or not a temperature of the battery is in a predetermined temperature area;
• a storage configured to store in advance a relation between the impedance slope and a battery state associated with the battery;
• and
• an estimator configured to estimate the battery state associated with the battery on the basis of the calculated impedance slope calculated by said calculator and the relation stored in said storage, when it is determined that the temperature of the battery is in the predetermined temperature area.