The aim of this paper is to develop a comparative experimental study on the electrochemical features of a Pb–1wt% Sb casting alloy in two different sulfuric acid solutions at room temperature. A water-cooled unidirectional solidification system was used to obtain alloy samples having different microstructural characteristics. These samples were subjected to tests in two different sulfuric acid (H2SO4) solutions: 0.5M and 5.0M H2SO4 and the resulting electrochemical impedance spectroscopy (EIS) plots, potentiodynamic polarization curves and an equivalent circuit analysis were used to evaluate the corresponding electrochemical behaviour. The experimental current density was found to be similar for all the examined Pb–Sb samples, and decreased with the increase in the cellular spacing, independently of the concentration of sulfuric acid in the solution. However, the EIS parameters demonstrated to be more affected by the scale of the cellular array in a 5M H2SO4 solution. Nevertheless, it is shown that Pb–Sb alloys having coarse cell spacings have higher potential for application as grid material in lead-acid batteries.