In 1936, while excavating the ruins of a 2000 year old village near Baghdad, archeologists discovered a mysterious clay pot. Inside the pot was a copper cylinder soldered with a lead-tin alloy and an iron rod suspended in the center, which showed signs of having been corroded by an acidic agent. This mysterious pot dated back to the early AD period but was almost identical in design to the electric battery which was invented by Alessandro Volta in 1799.
How is it possible that a complex battery was built in ancient Sumeria some 1,800 years before such a battery was invented?
Well perhaps someone living after 1799 traveled back in time and for some reason needed to make a battery (maybe in order to power their return trip). A person who has mastered time travel would surely have known about Volta's battery and would have known it was one of the easiest batteries to create in such a primitive setting. And perhaps the battery was left behind when the time traveler returned to his or her origin in the space time continuum.
It's an interesting idea at least.