You can cut piece batting into or around the edges by using quilt batting tape. Cut out any damaged batting, cut a piece to fit, and use the batting tape with an iron to fuse the edges together. That way you keep the batting type the same throughout. I would not try to mix fusible batting with Hobbs 80/20. I would just piece so it is all Hobbs 80/20.
If you don't have the batting tape, all it is is pre-cut strips of fusible nylon tricot.