Battery blowing voltage regulators "why"

Ok guys
I changed out the battery with a smaller cca battery I fhad in the shop. Problem solved.
I just want to know what could be wrong with a battery to cause this? I took it to auto zone where I bought it and had it checked. The clerk said the battery showed bad, but he couldn't say what was bad just that his machine said it was bad.
Any ideas?

big block

It has an internal intermittent short, batteries can do all kinds of things
like that. They can have/develop cracks in post connections & cell bridges that work
one second and not the next, pass a test and then not start 3 tries later,etc.
The alt. can put out 18V or so full fielded,if that happens repeatedly,even if
briefly you're going to burn stuff up.I've seen many batt.s subjected to shocks,as
in accidents, and if it required any serious repairs the odds were 50/50 it would
last.Even if it showed -0- damage and on the opposite end of the car I would
demand a new batt. from the ins. co. even if I had to pay it "pro-rated" for that
reason. Given you state "problem solved", get a new batt. dude, or make them
eat it if it has any warr. left. :coffee2: