BATTERY DIAGNOSTIC SYSTEM

A battery diagnostic system (1) includes a load history acquisition unit (51a), an interpolation processing unit (51b), a degradation estimation unit (51c), a degradation prediction unit (51d), and an output unit (51e). The load history acquisition unit acquires a battery load history of a used secondary battery (25). When a portion of constituent data of the battery load history is missing, the interpolation processing unit estimates and interpolates the missing constituent data using the rest of the constituent data. The degradation estimation unit estimates, based on the battery load history, a present degradation state of the secondary battery and a cause of degradation that has brought about the degradation state. The degradation prediction unit performs diagnostics by predicting, using a predicted battery load, the present degradation state and the cause of degradation of the secondary battery estimated by the degradation estimation unit, a predicted degradation state of the secondary battery that will occur in the future upon having been used in the use mode. The output unit outputs the predicted degradation state of the secondary battery predicted by the degradation prediction unit.