When batteries short internally they'll expand like that too. Often times they'll blow up not too long after. Had that happen in a truck a few months ago.... it went kaboom soon as the truck started up and it started charging (I told the guy he needed a battery and he declined.... oh well!)

Totally possible. The battery is under a cover, and in the 4 years Ive had my truck I never looked at the battery, it always worked fine so I left it. The battery felt weak when I tried to start it which is what prompted me to get a new one.