A theoretical model for the porous lead dioxide electrode is proposed on the basis of the macrohomogeneous model for porous electrodes. The structural changes during discharge, due to precipitation of lead sulphate, are considered. The two main structural effects, plugging of the pores and gradual insulation of the active electrode surface by the reaction product, lead sulphate, are both considered by relating them to the local degree of discharge. The numerical results show that, at high current densities, the discharge capacity is limited by both structural and transport restrictions. At the end of discharge a layer of lead sulphate crystals blocks the electrode surface in the outer layers of the electrode. The current can then neither be transferred across this insulated surface nor reach remaining active material in the inner parts of the electrode because of acid depletion, which is furthermore accelerated by the decreasing porosity.