I've made a cotton quilt top for my son, he wants fleece for on the back. Should I put batting too or can I just put the fleece on without batting?

You can do whatever you want. If you put batting in between the quilt top and the fleece, it might get too warm. So it depends on your "in hiding" climate!

ditto ... depends on what you want, though the fleece will do the batting job, if you want to not use it!

I wouldn't spend the money for batting. I would rather buy a light weight blanket and use that with the quilt. Remember how we are taught, to dress in layers when going into the cold.