You can also scuff the cells using a dremel and sanding drum. Just start in the middle of the cell, and work your way out in a circular motion. If you’re careful, you should not come in contact with the shrink. Once scuffed in, apply motor spray to a rag and wipe off all left over residue on the cells.
Retired from RC....
Quantum - St. Croix - Bass Pro Shops - XPS - Rapala