I've been very happy with my sealed Universal AGM batteries that I got from bestconverter.com.
http://www.bestconverter.com/Univers...ies_c_127.html
The factory battery racks in my 2015 Raptor didn't have enough height to go with 6v batteries so I ended up with 3 of the 12V 100AH model. They are big and heavy so check measurements. Getting them in on my unit took a bit of effort. Price wise I think they are definitely on the high end but ease of maintenance for a true sealed battery and life expectancy is much better than what I was able to get out of a standard battery.
There is a link to this website on the above mentioned website which I found very useful.
http://www.marxrv.com/12volt/12volt.htm