An estimation device includes: a derivation unit deriving a derivation history based on a current, a voltage and a temperature of a lead-acid battery; a first specifying unit specifying a specific gravity of an electrolyte solution; a second specifying unit specifying at least one of: a first degree of softening of a positive electrode material; a second degree of corrosion of a positive electrode grid; a third degree of sulfation of a negative electrode; and a fourth degree of shrinkage of a negative electrode material based on the specified specific gravity, the derived derivation history, and at least one of respective first-third relationships between the specific gravity, respective first-third histories and the respective first-third degrees, and a fourth relationship between a fourth history and the fourth degree; and an estimation unit configured to estimate a degree of deterioration of the battery based on the specified degree.