Exploding Audi

["Levis-Fithian, Jeff E" <LevisJE@LOUISVILLE.STORTEK.COM>]

Last night I got into my car (95 A6), turned the key, and heard a _very_
loud bang.  At first I thought it was the radio, since it sounded like a
speaker pop, but louder than any I have heard before.  Upon further
examination, I discovered that the battery under the rear seat (that my 3
week old son was sitting on!) EXPLODED.  The plastic casing around the
battery was cracked, the breather hose was blown off, and miscellaneous
plastic bits were laying around the battery, along with a couple drops of
fluid (acid?).  Has anybody ever experienced this before?  I can easily go
purchase a new battery, but I am worried about the root cause here.  Any
ideas?

Also, are there any alternatives to buying a battery from a dealer for $90?
The one from the local auto parts store ($50 Duralast) doesn't have a vent
hole, and I am worried about fumes building up under the seat and causing an
even bigger explosion.

Thanks

Jeff Fithian
95 A6Q 5sp with exploding battery option