The battery unit includes a storage configured to store (A1) and (A2) below, and a battery state estimator.



(A1): a table map OCV vs. SOC characteristics.
(A2): HF vs. SOC initial characteristics.




The battery state estimator estimates, based on (A1), a start SOC corresponding to a detected OCV at a start of charge; measures HF vs. SOC present characteristics and detects a peak of differential characteristics of the measured HF vs. SOC present characteristics during the charge; determines a SOC at the detected peak as a SOC(HF) based on (A2); calculates a charge capacity from the start of the charge to detection of the peak; calculates a SOC(OCV) based on the calculated charge capacity and the start SOC; and in a case where the SOC(OCV) deviates with respect to the SOC(HF) by an amount of deviation equal to or greater than a predetermined value, corrects (A1).