Not sure if this has been posted before but this scientist appears to be suggesting that low energy nuclear reactions (LENR) might be occurring in lithium batteries and that this might account for some instances of combustion.
http://www.slideshare.net/lewisglars...diseaug-6-2013
I should point out that the authors views do not accord with the general scientific consensus which says LENR is impossible. His company also claims to be trying to commercialise LENR for power generation. I understand he is one of the few people to have had a paper on LENR published in a peer reviewed journal.