I get the feeling it has to do with how wireless charging works. On a wire, a phone can regulate how quickly it takes charge or whether it does at all. I don’t think phones are capable of that with wireless charging, which is exclusively how I charged my pixel 5 at night.

So it would get to 100% and stay there for several hours every single night. I didn’t realize it was bad at the time.

It could always just be that I was unlucky and got a defective battery to begin with. No way to know for sure.