In 1938 Iraq, people found a set of clay jars, this jar can produce a small electric current when filled with some liquids, part of the people believe that this were ancient electric batteries, but some people rebut this argument. 
    First, because there need to be electricity conductors such as metal wires if it's a batteries, but there is no evidence that any metal wires located near the clay jars. Although there are no metal wires around it, but another possibility is that because the one who discover this clay jars is local people but not archaeologist, so the metal wires might be overlooked or through away because the local people is not aware of process during discovering.
    Second, the copper cylinders inside the jar look similar to the copper cylinders discovered in the ruins of Seleucia which is used for holding scrolls of sacred texts, so it might have the same application,  Although it have the same design, but people might design it for holding scrolls of sacred texts first, and discover anther use of it after it been design which is use for battery. 
    Last, ancient people don't have electricity devices, so there is no need to the battery. although