Been commuting on the bike recently and had a doozie this morning. First actual failure of the KTM since I bought it 4 years back.

Had a couple stops on the way to work today and on the second one the bike cranked half a turn then made a pop noise and everything went dark. Its sitting in a parking lot of a gas station atm and I'm now at work but this is what I found. Guy at work brought me some of my tools to do a quick attempt at a diag.

Battery new at the end of last summer, strong up until now and stored on a tender through winter.
key off voltage read 11v (first sign)
key on voltage read 3v (second sign)
headlight fuse installed I get no power to anything with key on
headlight fuse removed I get enough power to fire the dash up
doesn't even consider cranking
main fuses are both ok
all little fuses were ok
jumper cables installed on positive battery post and engine case bolt the bike would crank half turn then lose power (though they had a crappy connection due to being car sized cables that barely fit on the battery)
I have no burning smells or obvious signs of serious arcing/shorts
Battery vendor tested it and said it was dead so I bought a spare

Before I install this thing and risk frying another new battery. Is it possible my starter killed the last one? How can I test it? Positive/negative posts across the starter measured 1.5ohms. How likely is it for a battery to internally fry with zero lead-up issues or warning signs?

check ground