I have prewashed Warm and Natural but only for those quilted items I want to remain flat or with out the shrinkage. For regular quilts that I want a bit of crinkle .. I use it straight out of the package.
Warm and natural is one of the better battings ars far as not have a big cotton ball in the bottom of the washer when you prewash.
If you really want to pre wash , I soak mine over night , then agitate for only a minute or two --gentle cycle. I do spin dry , then pop in the dryer regular cycle.