I didn’t clean off the old adhesive, it seemed sticky enough, so I just press the new battery in and held it - seems ok. Might live to regret that though…
+1 for this. The video was really useful - I used a craft knife to release the clips. I found that once I’d done the first two at the bottom end, the rest came easily.
There was a perforated strip down the centre of the jacket, tearing this gave a handy tab to pull on. I heated the back of the phone with a hairdryer for 30 seconds and pulled gently - under consistent tension, it slowly came out.