I was leery of even trying to venture into replacing the battery on my Pixel 3a, but then after watching the instructions and an youtube video, I ordered the kit. Carefully and cautiously following the instructions, everything went smoothly and slowly. When all was done and the battery was presumably re-charged, I immediately tried turning on the phone. And there was just a black screen and - nothing. That was a big disappointment, but I decided to re-try everything again, step by step, leaving the phone "to rest for a day". And then, when I tried to turn on my "dead phone" after two days of just "resting", it miraculously "revived". It's been working perfectly well since then (end of May 2024). Where was the catch? In my eagerness to triumph after "I did it", I oversaw the sentence about the "(re) calibration of the battery" at the end of the whole process. It takes (some) time and it happened during the "rest" period.
Arthur Shi's Guide is perfect, ++it should be read and followed carefully++. In the case of my Pixel 3a I didn't have to apply heat (iOpener) to "open" the phone, just slowly and carefully used picks (labeled 1mm and 6mm with a Sharpie on picks). Thank you ifixit, thank you Arthur Shi.