A charger with a battery diagnosis function, the charger comprising: a DC-DC converter configured to apply a perturbation voltage to a battery when the DC-DC converter charges the battery in a charging mode or when the battery is fully charged; and a digital signal processor configured to: calculate equivalent circuit model parameters of the battery according to an output response of the battery with respect to the perturbation voltage, calculate a charging/discharging frequency, x, of the battery by using an ohmic resistance value, Rs, among the equivalent circuit model parameters of the battery, and calculate a residual capacity of the battery by using the charging/discharging frequency of the battery, characterized in that the digital signal processor includes a parameter analyzing unit, which is configured to calculate an ohmic resistance variation equation of a quadratic equation form Rs = A 1 + A 2 x + A 3 x 2, wherein A 1, A 2 and A 3 are the parameters of the quadratic equation, which expresses a relationship between the ohmic resistance value, Rs, and the charging/discharging frequency, x, and is configured to calculate the charging/discharging frequency, x, of the battery by using the following ohmic resistance variation equation: x = − A 2 ± A 2 2 − 4 A 3 A 1 − R S 2 A 3 and to calculate a residual capacity variation equation of a cubic equation form, which expresses a relationship between the charging/discharging frequency, x, and the residual capacity, Cm, and is configured to calculate a residual capacity, Cm, of the battery by using the following residual capacity variation equation: Cm = B 1 + B 2 x + B 3 x 2 + B 4 x 3, wherein B 1, B 2, B 3 and B 4 are the parameters of the cubic equation, and in that the perturbation voltage is a sine wave-type perturbation signal. a DC-DC converter configured to apply a perturbation voltage to a battery when the DC-DC converter charges the battery in a charging mode or when the battery is fully charged; and a digital signal processor configured to: calculate equivalent circuit model parameters of the battery according to an output response of the battery with respect to the perturbation voltage, calculate a charging/discharging frequency, x, calculate equivalent circuit model parameters of the battery according to an output response of the battery with respect to the perturbation voltage, calculate a charging/discharging frequency, x, of the battery by using an ohmic resistance value, Rs, among the equivalent circuit model parameters of the battery, and calculate a residual capacity of the battery by using the charging/discharging frequency of the battery, characterized in that the digital signal processor includes a parameter analyzing unit, which is configured to calculate an ohmic resistance variation equation of a quadratic equation form Rs = A 1 + A 2 x + A 3 x 2, wherein A 1, A 2 and A 3 are the parameters of the quadratic equation, which expresses a relationship between the ohmic resistance value, Rs, and the charging/discharging frequency, x, and is configured to calculate the charging/discharging frequency, x, of the battery by using the following ohmic resistance variation equation: x = − A 2 ± A 2 2 − 4 A 3 A 1 − R S 2 A 3 and to calculate a residual capacity variation equation of a cubic equation form, which expresses a relationship between the charging/discharging frequency, x, and the residual capacity, Cm, and is configured to calculate a residual capacity, Cm, of the battery by using the following residual capacity variation equation: Cm = B 1 + B 2 x + B 3 x 2 + B 4 x 3, wherein B 1, B 2, B 3 and B 4 are the parameters of the cubic equation, and in that the perturbation voltage is a sine wave-type perturbation signal.