[adciv]

I'd like to see some pictures if you can post them.

It sounds like you had an internal battery short. This can be caused by a piece of metal getting inside and causing the cells to conduct from one to another. The FTC battery cells are metal all around and conductive. If the insulation around them is worn away, it can short to the robot frame. One of the FTC teams I've worked with had a battery short to the frame of the robot and the there was a return path back to the battery which provided a short circuit. The path bypassed the battery fuse and the mishap caused a motor controller to catch fire.

For disposal, dispose of it as you would any NiMH battery (I think that's the correct type). Your local area should have some way of disposing of old batteries.