Here in the US there was an issue with some older iPod nanos getting scratched easily that led to Apple sending checks to owners of the device. Over in Japan the first generation nano has had a more serious issue.
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Apparently several fires have been linked to the iPod nano and overheating of its battery. Apple says that signs of overheating include deformation and discoloration. Anyone in Japan owning an iPod with one of those issues can return it for a replacement.
If a user fears that the battery will overheat Apple is offering to replace the battery. The first generation nano was offered in Japan from September 2005 until December 2006.