It was good of you to take the battery birds. They aren't usually bred for a long life but for egg production. Approximately 60% of the brown egg layers are ISA Browns which were developed for high laying capacity but usually burn out after a couple of years and most operations only keep them for around their fist year when they are the most productive. Good luck and have fun...
Hello and welcome to BYC, You found an Amazing Poultry Community to be a part of with many great knowledgeable members, who are more then willing to jump in and help you along your journey with any questions you may have.