Well if your iPod is charging and it is on but when you disconnect it from the charger and shuts it will usually mean you have one time left it on the charger way to long and it has killed the battery. Or if it is around 50% charged and you plug it in and charge it, it will mess up the battery. What you need to do is just let the battery totally run out and then wait for 10 or 15 minutes to charge it, then your all set.