Alkaline button batteries use Zinc for their anode, manganese dioxide as the cathode, and an alkaline electrolyte. Zinc, which is the activator in the anode, corrodes when dissolved in alkaline solution. When this happens, it becomes difficult to maintain the capacity of the unused battery. Zinc also causes electrolysis in the electrolyte, generating Hydrogen gas which causes increased inner pressure and expansion of the cell. For this reason, mercury, which is effective in suppressing Zinc corrosion, was added to the battery.