Japanese fans of the iPod who still have a first generation iPod nano lying around can get a free replacement from Apple if that gen one player suffers from overheating. The original nano was sold in Japan from September 2005 to December 2006.
The reason for the replacement according to Apple is that rare cases where the battery inside the iPod overheats to the point that it deforms and poses a risk of fire. Apple says if the first generation nano shows signs of overheating such as discoloration or deformation that the owner should discontinue use and contact Apple for a replacement.
Apple support will also replace the battery in units that are not showing discoloration or deformation if the user is concerned about overheating. Apparently there were several fires linked to the iPod nano in Japan prompting the replacement offer.