Apple has unveiled a worldwide replacement program for the first-generation iPod nano music player due to overheating battery issues, telling owners to stop using the product and get it replaced for free. \"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,\" said Apple in a notice posted late Friday on the support section of its official website.