A method is proposed for the characterisation of expander materials based on the comparison of the results of three different electrochemical techniques: electrochemical impedance, cyclic voltammetry and potentiostatic transients. The evaluation of the expanders performance carried out on the basis of the results of such techniques takes into account different important actions of the organic additives such as adsorption on lead and the kinetics of electrochemical reactions, which are all very important for the practical behaviour of the expanders in the negative plate of the lead-acid battery. The need of clarifying possible correlations between chemical characterisation and electrochemical tests is shortly discussed. This last point is mainly focused on the understanding of the action of the functional groups which are present in the organic molecules. (C) 2001 Elsevier Science B.V. All rights reserved.