METHOD FOR DETERMINING DROP IN CAPACITY OF SODIUM-SULFUR BATTERY

It is determined that a drop in the capacity of a sodium-sulfur battery has proceeded to an abnormal level when both the following expression (1) and expression (2) hold. Qe - Qn ¥ K1 ··· (1) where Qe: abnormal block depth of discharge; Qn: normal block depth of discharge; and K1: block abnormality determination setting value (integer constant), and Qe ¥ K2 ··· (2) where K2: depth of discharge abnormality determination setting value (integer constant).