Now this is a pretty extreme example of battery abuse however it certainly gave me a surprise.
A lot of us are now carrying much larger lithium polymer batteries as an FAA mandated backup to our Electronic Flight Bags (usually a tablet, e.g. an iPad). We are warned not to put the backup battery in checked luggage.
Fortunately, the FAA reassures us that damage to a lithium ion battery (they don't seem to yet distinguish the increasingly popular lithium polymer variants) is not dangerous:
While there is no explosion hazard associated with either kind of battery, the Federal Aviation Administration has studied fire hazards associated with both primary and lithium-ion cells, and their extensive research is publicly available. As a result of this research, the FAA no longer allows large, palletized shipments of these batteries to be transported as cargo on passenger aircraft.
The research also shows that an explosion will not result from shorting or damaging either lithium-ion or primary lithium batteries.
Safe Travel with Batteries and Devices | Transportation Security Administration
A colleague who does a lot of remote control helo hobby work showed me a cellphone video of his intentional destruction of a 'worn out' 6000 mAH LiPo battery. The pyrotechnics were impressive.
