An estimation device includes: an acquisition unit that acquires a voltage, a current, and a temperature of a lead-acid battery; a first deriving unit that derives a first SOC and a second SOC that are SOCs of a start point and an end point of an estimation period; a second deriving unit that derives a total amount of an overcharge amount in the estimation period; a third deriving unit that derives an actual measurement error based on a difference between the first SOC and the second SOC and the total amount of the overcharge amount; a first specification unit that specifies an estimation error based on the first SOC, the second SOC, and the temperature, and a relationship between the first SOC, the second SOC, and the temperature of the lead-acid battery, and the estimation error; a second specification unit that specifies an abnormality degree of the actual measurement error based on the derived actual measurement error and the specified estimation error; and an estimation unit that estimates generation of an internal short-circuit of the lead-acid battery based on the abnormality degree.