It is good you have a controller..

I sometimes use the term boiling or cooked when I mean gassing or electrolyte gassed off to where the loss of electrolyte has exposed the plates. It seems to be pretty well accepted description, right or wrong...

Last winter I had a 6V bank destroyed on a customers boat after he connected an unregulated solar panel, outside the cover & aimed at the sun, and left it there all winter.. I had fully charged the batteries, checked electrolyte level (did not need any), did a a specific gravity test on all six cells (sight refractometer), performed a conductance test and completed one hour of equalization @ 15.5V while I was there winterizing the boat. I then left the batteries 100% disconnected but fully charged..

When I got there to reconnect everything in the spring I found a 20W solar panel connected to the house bank. This panel is only about 9% of the banks capacity, in watts, and the bank is 225 Ah's...

In the fall the batteries had tested nearly perfectly, considering the age, and they put up 710CCA on my Midtronics analyzer. In the spring, after having the unregulated panel connected, they measured as SCRAP LEAD.... Just 2 CCA.... The battery cases were bulged, the positive posts were bulged and the batteries had approx two inches of exposed plate... They had been chronically over charged.

Despite my suggestion that the batteries would be fine, if fully charge and left disconnected, as they had been for the previous 6 years, the owner went back to the boat and installed an unregulated 20W panel after I completed winterizing.....

When I called him; "Well I read on the internet that a panel of less than 10%........." He now has a controller and a new 6V bank....