I did it myself with some kit bought online for a 2013 (I think it might have actually been specifically an iFixIt kit). Ungluing the battery took all of 15 min

I did it myself with some kit bought online for a 2013 (I think it might have actually been specifically an iFixIt kit). Ungluing the battery took all of 15 minutes and the plastic card jiggering was fairly trivial. I’m quite positive the actual reason for its high difficulty score is that actually reaching the battery basically requires completely dismantling the whole laptop — the battery is under the motherboard, and every little module has to be removed and taken out fully before the motherboard can go. And putting them back in, the connectors are ridiculously small and fiddly. The battery being glued was completely a non-concern IME.