If a battery freezes then you will see the tall tale sign of cracks in the case and no fluids inside after all of that ran out through the craked case after it warmed back up...
Don't believe you have a frozen battery. You do have a dead battery however and being a DEEp CYCLE it is tooast now since being sitting there all this time being discharged. Death of batteries start right away just when the charge state hits the 50% (approximately 12.0VDC) charge state.
We work hard here knowing what is going on with our batteries... Batteries are too expensive to have to replace them every year...
I probably look at my batteries every four or five days here and glance at the Meter panels to see their approximate charge status... My batteries will show 12.6-7VDC after being charged up and sitting for awhile. They seem to like to drop down to the 12.5VDC range and sit at that level for months just sitting there diconnected... When they drop to 12.2-3VDC I also will put a trickle charge on them.
My original battery bank was up and running in 2009 and is just now showing lower performance which is dropping down to the 50% charge state quicker than before... Looking to replace them this season... Out of my four batteries I have one go bad in 2009 becuase I was charging them with a single mode charger and boiled out my fluids.. I stopped using the ssecond one just recently in 2012 - it was not holding its charge like it should. The remaining two is just now starting to drop performance - One is good and the other one goes down to 50% charge pretty quick... Time for new batteries as all the special charging routines don't help any more...
Roy Ken