The battery cage system is a method of housing chickens for egg production, in which chickens are kept in small cages in large numbers. There are several types of battery cage systems, including:

1. Conventional battery cages: These are the most common type of battery cages, and they consist of small, wire-mesh cages stacked on top of each other in rows. Each cage is designed to hold several birds, and they are typically housed in large, warehouse-like buildings.
2. Enriched cages: These are larger than conventional battery cages and have some additional features such as perches, nest boxes, and scratching areas. Enriched cages provide more space and some additional opportunities for natural behaviors, but they still do not allow for the full range of natural behaviors that chickens would exhibit in the wild.
3. Furnished cages: These are similar to enriched cages but provide even more space and additional amenities such as perches, nest boxes, and litter areas. Furnished cages allow for more natural behaviors than conventional battery cages or enriched cages, but they are still far from ideal in terms of animal welfare.

It’s worth noting that many animal welfare organizations and advocates oppose the use of battery cages for laying hens, citing concerns about animal welfare, health, and environmental impacts. Alternative housing systems, such as free-range, cage-free, and aviary systems, have become more popular in recent years.