Battery is an item obtained in the 2014 Winter Festival event.
It is discontinued as of December 31, 2014.
Battery is given to one of the goblin elves in The Toy Factory Grounds in exchange for 4 Winter Festival Tokens. It currently serves no other purposes.
Like the other two collectible items from the Winter Festival, Battery can be found from any chest, monster loot bag, or whackable item, with the only exception being certain spider eggs and crates in The Crystal Crusade multiplayer mission.