Smith College Museum of Ancient Inventions: Baghdad Battery:

"The Baghdad Battery is believed to be about 2000 years old (from the Parthian period, roughly 250 BCE to CE 250). The jar was found in Khujut Rabu just outside Baghdad and is composed of a clay jar with a stopper made of asphalt. Sticking through the asphalt is an iron rod surrounded by a copper cylinder. When filled with vinegar - orany other electrolytic solution - the jar produces about 1.1 volts. "