These guys took a lithium ion battery (you know, like we all have in our cell phones) and forced it so far into over-charge that it exploded!
Obviously any properly functioning charger on an undamaged battery would not cause this type of reaction. In fact, all lithium batteries have a charge limiter (either on the charger or battery) to protect the battery. For this demonstration the charge limiting was bypassed. Even with all the precautions they took it seems like it was a bigger explosion than expected.
This was set up with a radio controlled model airplane battery. Check out the video and be thankful for those charge limiter.