Be very careful filling 6v golf cart batteries! You don't fill them to the "top ring" like you do a 12v standard battery. If you do, they will spill over during a charge cycle. Most recommend only filling them so that the plates have about 1/2" to 3/4" of cover.
An auto-fill system will likely overfill them.
If you need to know how I learned this, it's "been there, done that, ruined a tee-shirt (and a pair of jeans) cleaning up the over-flowed acid"!
Two weeks after I did it, a buddy of mine did the exact same thing, and got the exact same result.......
2014 RAM 2500 Laramie 4x4 Quad Cab w/Cummins Turbo Diesel, 2009 Rockwood 2607, and 3 'yaks!
300W of Suntech Solar, a Rogue MPT-3024 Controller, and a Xantrex PW2000 Inverter