J C Boyd, an early advocate of galvanism promoted his battery as having healing qualities for a host of ailments.
His pendants were the most commonly used in the late 19th century and there were a number of imitators. He patented his battery in America initially and shortly afterwards in England.
A small electric current is set up when metal are juxtaposed. It was knowledge of this phenomenon and an emerging understanding of the central role of electricity in nature and life itself which led to the belief that objects with galvanic properties would have a therapeutic effect on illness, ostensibly in whatever guise it manifested itself.