Characterisation of expander materials has been obtained by comparing the results of three different electrochemical techniques: cyclic voltammetry, potentiostatic transients and electrochemical impedance. It is shown that 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 kinetics of electrochemical reactions. Seventeen different organic substances have been tested including both commercial materials used in the lead-acid battery industry, and other materials presenting physico-chemical similarities to known expanders.