Alright guys I need advice. I pulled a Bill Dance and went overboard with a battery. The battery was un-retrievable for about 18 hrs in roughly 12ft of water and with the help of a really good friend we finally recovered it. After the recovery I hooked it up to a 55lb thrust trolling motor and it worked, however I hear sloshing around in the battery. The battery said it is accessible for maintenance but I have no idea what to do. Any advice would be great, thanks!

Take it to your local auto parts store or mechanic and have them load test it.  If it passes, keep it for a little while and see how it goes.  If you think its seal was bad and water got in it, dispose of it (properly, of course) and get a new one.

IF the battery is lead/acid there will be "sloshing around" since it has liquid inside whether it has been submerged or not.

If it's lead/acid, open the covers on the top with a flat head. Dispose properly of what's inside. Go to auto part store and buy new battery acid. I think it's $10 a bottle. Pour in in until over the metal in the battery. Give a full charge on 2 amps. Should be good to go. 

I would check the cells by popping the tops off and checking the acid levels inside.  If the acid is contaminated (IE if there is muddy water in the cells or off color liquid) dispose of the battery and buy a new one.  You're not going to be able to drain and save it as there is no way to remove the dirt and film from the water it was submerged in.  Now if it looks good and the liquid is clear (shine a flashlight in there to see), be very careful when doing this to avoid any splash back and make sure you don't have it on the charger when you do this.  If it's clear and you see no issues but the cells are low, go buy some DISTILLED water.  Fill to just above the lead plates, and put on the charger.

That is ONE way of topping off the water-levels.  Just kidding.  I would have probably forgotten to let go of the battery and gone down with it.