With four huge AGM batteries I need to keep them from sliding around. I was originally going to move the batteries to under the settee, to lower and centralize the mass, rather than have it all sitting on the transom, but I decided to just use two, not four, and put one on each side in the lazarettes. These trays work just fine with two up or one on the side. The idea is to secure the tray to the floor and to keep the batteries from shifting when heeling.
I started the process by making a pair of mock-up batteries so I could easily move them around, a lot easier than the 116lb of each actual battery.