Alternating current impedance spectroscopy (ACIS) was performed on commercial sealed Ni-Cd cells. A method previously developed in the literature was modified to determine the state of charge of sealed Ni-Cd cells by obtaining the impedance spectrum in a wide frequency range. The impedance parameters were sensitive to state of charge at low frequencies. A modified Randles’ circuit was used to fit the impedance data. Appropriate modifications were made to account for an additional high frequency are or a low frequency finite diffusion element. The effect of the state of charge on the equivalent circuit parameters was determined.