For me, actually replacing the battery wasn’t too bad, but I ended up using too much isopropyl to clean off the old glue, and it seeped under the display and ruined it. Wish Apple didn’t use so much glue. It massively impedes repairability, which is not very environmentally sound. My iPad was perfect apart from the battery - it’s now got a perfect battery but the iPad is ruined :-(

I followed these instructions and used 99.9% isopropyl alcohol to clean off the glue around the display - but the isopropyl leaked under the screen and ruined it! Replacement screen more than the iPad’s worth. Use tiny amounts and don’t allow for any seepage, or try to manage without and just carefully scape. My iPad’s now a write-off… :-(