READ THE PACKAGE DIRECTIONS!!!!
I know I just yelled - but that is the best place to find information.
I wash warm and natural - I prefer a flat look - and once because one of my cats anointed it. I wash warm and natural on a short gentle cycle and dry it in the dryer on a gentle cycle until it's almost dry.
I also have shredded a couple of battings - There was no label on them and I thought they looked washable. The ended up like shredded kleenex!
Again - it depends on what you are starting out with and what you want to end up with.
I think MOST battings do not need to be washed - especially if you don't mind some shrinkage.