I found an easy way to piece batting (read it on here a while back I think). I put my 2 pieces together, cut with rotary cutter, pin so it doesn't shift, stitch over the edge using a blind hem stitch with the straight stitching going just off the fabric and the zigzag stitch catching the batting. Open it out and gently smooth the bump down with your finger. I found that it is much quicker and easier to handle. Give it a shot on some scraps and see what you think.
