To minimize the migration of mercury droplets when discharging cadmium/mercuric oxide (Cd/HgO) cells, silver powder is often blended with HgO powder in the cathode to promote formation of a solid Hg-Ag alloy. Even though only high purity materials are used, open-circuit cell voltages are much higher than what is normally observed when Ag powder is not present. There is also a significant variation in the open-circuit voltage (OCV) of a given lot of Cd/HgO cells. We hypothesized that this high OCV and cell voltage variation is at least partially attributed to uncontrolled very small quantities of mercury present in the HgO. The potential variations arise from the reduced activity of mercury in the Hg-Ag alloy. The experiments that were carried out and reported here support this hypothesis.