By electroplating lead–tin alloys on a lightweight substrate material, such as glassy carbon, it is possible to obtain less dense electrodes with good contact between the active material and the substrate. The former is especially important for the lead–acid battery since it has relatively low energy density compared to many other battery systems. In order to obtain higher power densities for applications in, for example, electric or hybrid vehicles, the weight of the battery needs to be minimised. In the present investigation, the oxidation of electrodeposited lead–tin alloys in 5 M H2SO4 was studied as a function of tin concentration. The alloys were prepared by electrodeposition and the oxidation behaviour was studied by the means of cyclic voltammetry. Microstructural information on the deposited layer was obtained by scanning electron microscopy (SEM). The experimental results show that electrodeposited lead–tin alloys contain a supersaturated solid solution phase with up to 12 at.% Sn. Oxidation of this phase in 5 M H2SO4 leads to the formation of a PbO phase with increased conductivity compared to pure PbO. In addition, the amounts of PbO and PbO2 decrease with increasing amounts of tin in the alloy and for high tin alloys, where a bulk tin phase is present, no PbO phase is observed.