Constant load vs constant current EIS study of electrochemical battery discharge

An experimental method to measure the impedance of electrochemical batteries during discharge has been developed. The method uses classical impedance-measurement apparatus and current perturbation to control a battery discharging into a constant load. Impedance measurements were carried out on sealed Ni-Cd cells with a capacity of 0.65 Ah using the classical modulated-current method and the new proposed method. The results are compared for cases in which both methods may be used. Impedance measurements carried out using the new method are also presented for sealed lead-acid cells with a capacity of 25 Ah and battery discharge currents greater than the maximum current that the regulation system could supply. These measurements show that the proposed method may be used with classical impedance-measurement set to test high-capacity and low impedance batteries during discharge into a constant load.