The first generation iPod Nano may overheat and pose a health and safety risk. Affected iPod Nanos were sold between September 2005 and December 2006. This is due to a flawed battery used by Apple from a single battery manufacturer. Apple recommended that owners of affected iPod Nanos stop using them. Under an Apple product replacement program, affected Nanos were replaced with current generation Nanos free of charge.

What part of the iPod Nano was the cause of the overheating issue?