STATE ESTIMATION METHOD, STATE ESTIMATION DEVICE, AND STORAGE MEDIUM STORING A PROGRAM

A state estimation device includes a first acquisition section, a derivation section, a second acquisition section, a computation section and an estimation section. The first acquisition section acquires measurement data and states of a reference rechargeable battery before and after a test that causes deterioration to progress. The measurement data is impedances at respective frequencies measured by an impedance method, and the states are found in advance. The derivation section computes peak frequencies before and after the test from arc-shaped curves in graphs plotting the impedances at the respective frequencies represented by the measurement data, and obtains a model representing a relationship between peak frequencies and states. The second acquisition section acquires measurement data of an estimation target rechargeable battery, which is impedances at respective frequencies measured by the impedance method. The computation section computes a peak frequency from an arc-shaped curve in a graph plotting the impedances at the respective frequencies represented by this measurement data. The estimation section uses the model to estimate the state of the estimation target rechargeable battery from the peak frequency of the estimation target rechargeable battery.