iOS 9.3 is coming in the Spring and will introduce Night Shift as well as a number of other new features.
iPod Battery Replacement Details from Apple
- If your iPod fails to hold a charge and it's more than a year old, you may need a new battery. Click Continue to order iPod battery service for $99 USD. This program is not available in Europe at this time.
The page warns that "iPod equipment that is sent in for battery service or service requiring other repairs will be replaced with functionally equivalent new, used, or refurbished iPod equipment. You will not receive the same iPod that was sent in for service."
According to information available to MacRumors, engraved iPods may simply have a longer turnaround.
The program appears to be now available.