Inspection, cleaning, servicing done. Battery number 2 and 3 had a little bit of deposits on the plate above the cells when I took the cover off. It didn't look significant, but will keep an eye on them. Water levels were good (after 10 months of 24/7 use). Static/disconnected voltages on the batteries were all resting at 12.8. Which is good. Wiped everything down real good, checked cables, cleaned terminal ends, and replaced some minor hardware. Overall, went well...took about 2 hours. Batteries are Wal Mart Everstart MAXX 29DC deep cycle marine.
UPDATE: It is good to "stir" them or equalization after a full charge. Some solar charge controllers can't do this. I hooked up my Schumacher SSC-1500A-CA Ship 'N' Shore 15 Amp charger and it brings the voltage up to 15.5 (instead of 14.5v). I leave it at 15.5v for about 3 hours. You can hear the six batteries "gurgle" but no water boils out. This will help with with sulfation and incorrect voltage readings. Essentially, you bring your batteries to 100% charge when you do this. I am also going to try and bump up my solar charge controller voltage to 15.2 or so instead of 14.5v.