The paper describes the principles of cell impedance measurement method, which, unlike other impedance techniques used for cell examination, operates on-line. In order to present the capabilities of the proposed method, experimental results are shown. The conducted experiment was cyclic charging and discharging of the lead cell in 4.8M H2SO4 with simultaneous impedance measurement. The variations of electric parameters, obtained as the result of impedance spectrums analysis, are highly correlated with the state of charge, as well as with the number of cycles.