Cadmium sticks, or mercury-mercurous sulfate reference electrodes, have been widely used in the past, in order to measure half-cell potentials in lead-acid batteries. The present paper presents experimental data obtained with a new type of reference electrode, based on the Ag/Ag2SO4 couple. This reference electrode has a reproducible and stable electrode potential, situated 38.4mV positive with respect to that of the Hg/Hg2SO4 couple. Ag/Ag2SO4 reference electrodes allow a precise evaluation of diffusion potentials (concentration cell voltage) in sulfuric acid solutions.