Impedance spectroscopy is a promising tool for the modeling and diagnosis of industrial batteries. This paper discusses methodological questions connected with the measurement and interpretation of the impedance of such batteries, especially nonlinearity, voltage drift, stability, reproducibility, half-cell measurements, model structure and parameter extraction with respect to quantities like state of charge (SOC). On the basis of this discussion, a specialized impedance spectroscope for industrial batteries has been developed, as well as modifications of the standard electrochemical impedance spectroscopy (EIS) algorithm. A mini-cycle technique is suggested that gains additional information compared to classical measurements with continuous de current offset. Impedance spectra from lead/acid batteries for different de currents, SOCs, and temperatures are presented and analyzed. Reference-electrode measurements allow for separation of the half-cell impedances. Emphasis is placed an the limits of experimental reproducibility due to "history" of the battery. (C) 2000 Elsevier Science S.A. All rights reserved.