Do you have any data to back up that statement of did you just make it up?
You just have to read the forums. We hear everything from first generation iPods still going (as one on this thread wrote) to as little as 18 months. But it's a moot point since, as I said, batteries failing in warranty are replaced for free. Those failing after warranty can be replaced for $30 without worrying about violating a warranty that no longer exists (you seem to have a hard time grasping that concept).