Found in 1938 by a German archaeologist, the ‘Baghdad Battery’ could be 2,000 years old, and consists of a clay jar, a copper cylinder and an iron rod. If filled with a weak acid, like vinegar, the combination produces around 1 volt. Yet while even some experts refer to it as a battery, its true origin and purpose remains unclear. One idea is that it was used for electroplating objects with precious metals.