I place two pieces of batting side by side- not overlapping just up against each other then using a wide- long zigzag stitch I stitch the two pieces together. This has worked for me for 20+ years. It’s quick and I can piece as many pieces as I need to in order to reach the size I need. It does not show at all in the quilt. You can not tell once the quilt is quilted that the batting was not a whole piece