Has anybody tried heat to loosen battery glue?

The idea is to heat the glue, not the battery. These glues usually soften at a relatively low temperature: heat-shrink gun, not paint stripper!

If it works, it's better than a putty knife, which is the solution already offered here. If you short one of these batteries it gets plenty hot all by itself. Certainly it is safest to replace the whole assembly; only a DIY will try otherwise, so it's as well the DIYs know what's involved first.

Methylated spirits is also an easy way to manoeuvre the battery out just use a q tip and gentlly loosen it out using a dropper is quite helpful also

I just replaced the battery pack on my MacBook Pro (Retina, Mid 2012) 15" and I looked at Youtube for help... One guy was using canned air (Dust-Off) with the can upside down so the cold liquid would get underneath the battery -- making the adhesive brittle, and then snap! The battery releases. http://www.youtube.com/watch?v=DPqrmt-Ic... Also another trick is instead of using the iFixit adhesive remover which I believe is acetone I used tried and true "Carpel-O-Peel" adhesive remover -- far less noxious. and worked even better at removing the residue AFTER I had removed the battery pack with a small narrow spatula/cake knife/putty knife. I also used the string method on a couple of batteries -- that works too especially with the cold dust-off liquid. Instead of string I found that edge trimmer cord (RYOBI 0.80" twisted bulk line from Home Depot AC04138 and AC04139) was even stronger but I had to get the battery started with a spatula to fit the monofilament underneath and around the battery.