I tried the heat up and pry method but quickly gave up. Instead I found that using a piece of strong thread (or dental floss) and alternately sawing one way then the other worked incredibly well and was really painless. It took about a minute to get the battery free so I’d strongly recommend trying this approach before you try prying the battery.
Here’s what I did:
1) I used tweezers and fed the thread under the bottom inner corner (where the battery cable is),
2) I slowly worked the thread along the bottom edge of the battery using the tweezers until it was under the far corner. I kept a little tension on the side that was already in place so it wouldn’t pull out.
3) I made sure I had plenty of slack on each side and then I pulled it in tight.
4) I took hold of the thread on each side in turn, wrapped it round a finger (with a piece of cloth to avoid cutting myself. Then I pulled it across and down the sides of the battery. It took about 3 pulls on each side to cut the glue completely.
This was definitely the fiddliest bit of the whole reassembly.
After trying the slide in and then press method many times without success I ended up feeding it in directly with the tweezers, carefully angling it back up into position, then clipping it down. But the whole thing took at least 5 minutes. And my shaky hands didn’t help matters!