Apple has announced an replacement program for the first generation iPod nano following potential safety risks that have arisen due to issues with overheating.
This issue has been traced to a single battery supplier that produced batteries with a manufacturing defect. While the possibility of an incident is rare, the likelihood increases as the battery ages.
Apple recommends that you stop using your iPod nano (1st gen) and follow the process noted below to order a replacement unit, free of charge.
Note: This battery issue is specific to the iPod nano (1st gen) and does not affect any other iPod.
Apple has posted a support page detailing the replacement process. Link below.