An estimation device comprising: an acquisition unit configured to acquire a voltage, a current, and a temperature of a lead-acid battery; a first deriving unit configured to derive a first state of charge and a second state of charge that are states of charges of a start point and an end point of an estimation period; a second deriving unit configured to derive a total amount of an overcharge amount that is a difference between an amount of charge and a discharge capacity in the estimation period; a third deriving unit configured to derive an actual measurement error that is a difference between a difference between the derived first state of charge and the derived second state of charge and the derived total amount of the overcharge amount; a first specification unit configured to specify an estimation error based on the derived first state of charge, the derived second state of charge, and the acquired temperature, and previously obtained and stored relational data representing a relationship between the first state of charge, the second state of charge, the temperature of a lead-acid battery in which an internal short-circuit and a minute short-circuit are not generated, and a previously obtained estimation error derived based on a difference between the first state of charge and the second state of charge and a total amount of an overcharge amount of the lead-acid battery in which an internal short-circuit and a minute short-circuit are not generated; a second specification unit configured to specify an abnormality degree of the derived actual measurement error based on the derived actual measurement error and the specified estimation error, wherein the abnormality degree of the actual measurement error is a ratio between the derived actual measurement error and the specified estimation error; and an estimation unit configured to estimate generation of an internal short-circuit of the lead-acid battery when the abnormality degree of the actual measurement error is out of a predetermined range. an acquisition unit configured to acquire a voltage, a current, and a temperature of a lead-acid battery; a first deriving unit configured to derive a first state of charge and a second state of charge that are states of charges of a start point and an end point of an estimation period; a second deriving unit configured to derive a total amount of an overcharge amount that is a difference between an amount of charge and a discharge capacity in the estimation period; a third deriving unit configured to derive an actual measurement error that is a difference between a difference between the derived first state of charge and the derived second state of charge and the derived total amount of the overcharge amount; a first specification unit configured to specify an estimation error based on the derived first state of charge, the derived second state of charge, and the acquired temperature, and previously obtained and stored relational data representing a relationship between the first state of charge, the second state of charge, the temperature of a lead-acid battery in which an internal short-circuit and a minute short-circuit are not generated, and a previously obtained estimation error derived based on a difference between the first state of charge and the second state of charge and a total amount of an overcharge amount of the lead-acid battery in which an internal short-circuit and a minute short-circuit are not generated; a second specification unit configured to specify an abnormality degree of the derived actual measurement error based on the derived actual measurement error and the specified estimation error, wherein the abnormality degree of the actual measurement error is a ratio between the derived actual measurement error and the specified estimation error; and an estimation unit configured to estimate generation of an internal short-circuit of the lead-acid battery when the abnormality degree of the actual measurement error is out of a predetermined range.