Update: 7/10. Taking the back off went easily/smoothly after lying on a 3D printer bed (@80C) for about 10mins, then using a hot air gun (@90C) and a metal spudger and plastic picks to gently break the adhesive holding the back to the body.
No issue removing the inside cover and pulling out the battery.
Having a replacement adhesive gasket/tape is a good idea when re-assembling though. The original guide didn't mentioned this.
