before I put the entire piece of ''raw'' batting in the washer/dryer, I would cut out a 12 inch piece and see what happens!! I think the top and backing fabric are needed to hold the batting fibers together.....
I never pre-wash any fabric or batting and have very little shrinking issues....but I LOVE the old fashioned 'wrinkled' look that you get after that first washing and drying of a finished quilt