Apple launched a worldwide replacement program for first generation iPod nanos on Friday that may have defective batteries. The units in question pose a potential safety risk thanks to a manufacturing problem that could cause the batteries to overheat.

Some first gen iPod nanos have defective batteries

In an email to iPod nano owners, Apple stated:

Apple has determined that, in very rare cases, the battery in the iPod nano (1st generation) may overheat and pose a safety risk. Affected iPod nanos were sold between September 2005 and December 2006.

The likelihood that the defective batteries will overheat increases with age, and the affected first generation models in the replacement program are over five years old now.

Apple has a Web page set up where first generation nano owners can see if their unit is eligible for replacement. Getting your replacement, however, won’t be quick because Apple is saying it will send out your not-so-hot iPod about six weeks after you send in your current model.

Assuming your iPod nano is eligible for replacement, Apple assign will send you a box for shipping and will give you a Repair ID number so you can track your iPod’s status.