The invention discloses an on-line judgment method for capacity of a
backup storage battery. The prior storage
battery capacity measuring technology is lagged. The on-line judgment method for the capacity of the
backup storage battery comprises the following steps: obtaining a corresponding relationship between the
internal resistance and the capacity of the storage battery through actual measurement, setting the
internal resistance of the battery obtained according to the capacity of the storage battery from the corresponding relationship as R1, setting the
internal resistance of the storagebattery according to the actual measurement as R2, and calculating a reference value R0 of the internal resistance according to the following formula: R0=
omega R1 + (1-
omega) R2, wherein in the formula, the
omega is
a weighting coefficient, the measured current internal resistance of the storage battery correspondingly searched from a graph obtained through the actual measurement is Ri, then the percentage of
delta R is equal to (Ri-R0) / R0, and the current capacity range of the storage battery can be determined by a corresponding relationship table of the actual measurement according to the numerical value of the percentage of
delta R. The method is used for on-line measurement for the capacity of the storage battery.