Has anybody tried heat to loosen battery glue?
The MBP Retina teardown uses brute force on the battery. Have you tried applying heat?
I would apply a heat-shrink style heat gun to the metal opposite whatever is stuck, right at the location where I'm prying. Do not directly heat the battery.
I haven't got an MBP Retina, but I've noticed the adhesives used in the old MBP respond to heat very well.
FWIW. Try this before solvent, which was suggested in another query. (Then try Goo-Gone, if you can avoid contaminating other components.)