I was having the impression that my phone (Pixel 4) battery is already low on capacity (and a battery monitor calculated a capacity of 61%) so I ordered a new one and followed a tutorial on how to replace it. It was rather easy.
Now with the new battery I have some strange behavior that I can't really solve but it is reproducible since days:
When my phone reaches around 40-45% while using, it shuts off. It doesn't shut down like it does when it is really on low battery, it simply dies. It also dies in a way that I can't trigger the booting process. I have to connect it to a cable, wait for the % to show up on the screen and then I am able to boot it. When it is finally up and running, I have often a completely different percentage shown in the top. Sometimes 50%+ (which means when it hits 40-45% again, it shuts off again). Sometimes (like right now) it showed 45% before booting and when booting was finished, it showed 18%.
So now I thought I need to calibrate it (and as I have read here, it is even only a myth). Anyway I tried it nonetheless. Drained it until it never even showed the boot logo again, then charged it until 100% while still being off. Issue persisted. I drained it again and charged it fully while being on. Still the same "shut off" around 40%.
One additional thing I noticed: My device lives like an hour at 1% capacity (no extreme power saving active!) before it shuts down, so I really have the feeling that the percentage is wrong/off.
Is the new battery broken? Would it help for me to make a full reset of my phone? Any ideas what I could try?