My trailer came with only 1 battery but the tray was big enough for 2.... kind of. I had to cut the handle off one side of the battery box so they would fit on the tray together.
As you shop for batteries be sure you know the terminology and get the right one(s). I learned the hard way that all batteries aren't created equal. You ultimately was a true deep cycle. There are hybrids that are cheaper but aren't nearly as good. The junk that came with my 2013 TT failed after about 1.5 years. I replaced with the two Heavy duty full deep cycle and it's awesome. I think they were around $100 each at Walmart.