Battery hens are laying hens who are confined in battery cages for the duration of their short lives. A number of factors combine to make the battery cage environment extremely uncomfortable for such hens, and some animal rights organizations have vigorously protested the practice of keeping hens in such cages. Most eggs in the market are produced by battery hens, unless the packaging on the carton explicitly states otherwise.

The earliest version of the battery cage was developed around the 1930s, and it quickly became a runaway success in the poultry industry. Several things distinguish a battery cage, also known as a laying cage. The first is the slanted floor, which is designed to allow eggs to roll out of the cage and onto a collecting conveyor belt. The cage is typically also all wire, allowing droppings and feathers to fall through the floor of the cage and onto another moving conveyor belt.

Food and water are delivered to battery hens using large conveyor systems, which deliver set amounts at specific intervals. Depending on the farming practices being used, the food may be supplemented with antibiotics to forestall infection, a common problem in battery hens, and the food may also be amended with vitamins and minerals in an attempt to get the hens to produce more eggs.

Perhaps the most distinctive feature of the battery cage is the size. Most battery cages are barely larger than the hens they contain, and in many instances, hens are unable to move or turn around. Typically, battery hens are installed in battery cages within weeks of hatching, and they spend around nine months in cages before being disposed of because they are no longer productive.

Like many animals, chickens can develop some curious responses to stress. Many battery hens, for example, will attempt to attack each other through the wire. As a result, most commercial egg producer debeak their battery hens periodically, removing their beaks with a heated knife so that they cannot attack each other. The hens may also throw themselves against the bars of the cage or wedge body parts into the wire, in some cases severely injuring or killing themselves.

Several nations around the world ban the practice of keeping hens in laying cages, under the argument that it is inhumane. It may also be unhealthy; confined conditions are a breeding ground for bacteria, which can be transmitted through the eggs of the battery hens to human consumers. Such bans can sometimes be disingenuous, as they do not ban caging outright, but rather the practice of using extremely small cages. Many animal welfare groups would like to see free range farming adopted as a universal practice, allowing chickens to live more natural lives outdoors, rather than being confined.