a storage battery system includes : a secondary battery ; a holding member comprising a flow channel of a cooling medium for cooling the secondary battery , which holds the secondary battery ; a medium temperature measuring unit that measures temperatures t 1 and t 2 of the cooling medium at two locations in the flow channel ; a battery temperature measuring unit that measures a temperature t 3 of the secondary battery ; and a judging unit that repetitively calculates a coefficient α and that judges a cooling performance of the secondary battery based on a variation of the coefficient α , the coefficient α being defined as /, /, or /.