Caged hens spend their relatively short lives of eighteen months confined to a cage from the time they hatch to the time they leave the laying shed. The reason for the short productive period is purely economic as once the hen has fulfilled one annual egg laying cycle it needs to rest and regenerate the laying organs. The cost of feeding and housing the hen while it's resting is greater than the cost of raising a pullet and an adult hen usually produces less eggs and bigger eggs in its second year.
Caged hens have continual access to fresh water through a drinker nipple attached to the cage. Water is essential for good egg production. A properly balanced diet is fed fresh several times a day using automatic feeders. This stimulates the hen to take an interest in the feed arriving to check for its favortite bits which aids egg production. Importantly each hen is part of a small group within the cage which allows it to socialize in a way similar to chickens in the wild from which it is genetically derived.
Many egg producers like to keep their hens in cages because they can manage them better for diseases. Its easier to pick a sick hen from a group of six than a group of hundreds. Seperating the hen from the group is simple in a cage but catching a hen from a large flock is stressful and can lead to injury and a drop in egg production.
Hens can be very savage at times if they sense a weakness in one of the flock. With many hens picking a weak bird the end often comes before the farmer can intervene. Small flocks in a cage reduce these occurances.