I have never and will never prewash my batting. I learned from my mother - Warm and Natural - finish up the quilt, throw it in the washer, hang it out to dry - almost - then throw it in the dryer. Turns out perfect every time. No problem. I always wash my sashing, backing, border and binding, but never wash the pieces I use for making the blocks. I like the old fashioned look to it. HAve never had a problem. Actually, it is totally what the quilter wants to do - I guess it is "My Quilt - My Rules. I still have a lot to learn yet - more easier ways to put a quilt together for one - everything else for another.
Happy Quilting. Edie