The iPod that I put in my pocket is on fire

It seems that the iPod (apparently like an iPod nano) that was in my pocket suddenly blew up and broke.

The movie is from the following.
Breitbart.tv >> 15 Seconds of Flame: iPod Ignites in Man's Pocket

This owner is Daniel Williams.


This is a pocket


What was in the pocket


The iPod which blown up a flame of unknown cause has become like this



What is the cause ...?