http://xkcd.com/651/

I have seen this comic strip from a popular site. It tells of a person in an airport with his water bottle taken away by security. The person then asks that why are they letting people carry laptop batteries. He says that if he overvolted the battery and if the cells are breached, the explosion will be sizeable. If you hover your cursor above the comic strip, an author's comment will appear, saying that a laptop battery contains the energy roughly released by a hand grenade.

It’s true. The difference is that the grenade releases its energy faster than the battery.

I remember my physics teacher telling my class something along the lines that a typical meal contains the same amount of chemical energy as half a stick of TNT, and the difference was just in how fast we can get them to release it.