If your battery stops charging and you have to replace it, the easiest thing to do is to contact Apple or go to your local Apple store. If your iPod is out of warranty, there will be a charge for it though. There are other repair shops that will replace your battery for you and their prices are sometime lower, however you would have to find one online or in your area that will complete that service for you. It is possible to replace the battery in your iPod alone by purchasing a kit. It’s important to backup your iPod before you start though, just in case something goes wrong.