Heh... I'm calm... I know Paul's threads are a bit special...
Um... To clarify... If you wan't heating included in the battery pack, don't use LiFePO4 chemistry... It's the most stable one... It goes "hiiiissss" and lets out the magic smoke... Not that interesting at all...
LiPO is by far the most interesting one...
I have so far managed to destroy 3 toy airplanes and one very, very small helicopter when charging LiPO's... And made one kitchen table unusable, or well, the significant other deemed it so based on the burn marks... To me it still looks like a table, but what do I know...
The Li-Ion one's don't catch fire very often... It takes a lot of hard work to make them blow up even half as spectacular as LiPO's... Like hammering nails into them, or hitting them with hammers... If you just abuse them with a charger they mainly tend to wave bye-bye and die quietly...