For me, the battery removal was probably as difficult. maybe more so than removing the back or mid-frame. The adhesive on the left side woudn’t let go and the plastic pick couldn’t reach the left-side adhesive to release it. I finally got it through perseverance though.
Coincidence. Batteries ship without a full charge.
If you’re really slow and careful (or really lucky like I was), the entire adhesive strip will stay with the glass and none of it stays on the mid-frame. I didn’t have to replace the adhesive because there was only one tiny lifted area on the glass that I was able to put back into the correct position using tweezers.
I did apply more heat around the mid-frame as well as the back-glass though. Since the mid-frame is metal, it sinks heat and the adhesive doesn’t melt until the frame gets hot enough.
When I did my battery, the adhesive stayed almost 100% on the back glass and was still in good shape. What didn’t remain attached only lifted slightly and I was able to coax it back to its original location with tweezers. I didn’t bother to remove and replace the adhesive layer because mine was still good. I set the glass out of the way where it wouldn’t get dirt on the adhesive while I finished the battery swap. I added some additional heat (hair dryer) after reattaching the glass to make sure the adhesive made the best seal.