 Original battery cages extended the technology used in battery brooders, which were cages with a wire mesh floor and integral heating elements for brooding chicks.The wire floor allowed the manure to pass through, removing it from the chicks' environment and reducing the risk of manure-borne diseases.Early battery cages were often used for selecting hens based on performance, since it is easy to track how many eggs each hen is laying if only one hen is placed in a cage.