I just came across this!!!
Apparently people invented the battery around 248 BCE! It's called the Baghdad Battery. This is an amazing energy source. I just can't believe something I thought was so modern has been around for so long.
About a dozen have been discovered and no one really knows what they were used for. It's a mystery.

World Mysteries - Strange Artifacts, Baghdad Battery

http://www.world-mysteries.com/sar_11.htm

In 1936, while excavating ruins of a 2000-year-old village near Baghdad, workers discovered mysterious small vase. A 6-inch-high pot of bright yellow clay dating back two millennia contained a cylinder of sheet-copper 5 inches by 1.5 inches. ...