A mercury battery is a primary cell. It has similar performance to, but is much cheaper than, silver oxide batteries. Its disadvantage is that it contains toxic mercury, which pollutes the environment. This battery uses the oxidation of zinc by mercury(II) oxide to generate electricity. It has either sodium hydroxide or potassium hydroxide as the electrolyte. Mercury batteries used to be common but have become increasingly restricted.
Some advantages of mercury batteries are their very long life and steady voltage.