Battery percentage jumps

Hi, I have an IPhone 11 Pro for over a year (out of warranty) now. Since a few weeks, I‘ve experienced some weird battery jumps and I really don’t know what to do.

Sometimes my battery is 100% and stays there for an hour of using und than starts to drop very fast to (what I’m assuming) the real level. Mostly it is something around ~95% This problem is not exclusive to the 100%, it generally happens in the 80-100% and the 20-0% zone.

A problem which has occurred at the same time is that my IPhone battery increases without charging ~max. 5%. Like the other problem, it happens when I’m in the 80-100% and the 20-0% zone.

The last problem I‘ve got is, with all these problems occurring, when I charge my phone -sometimes it’s stuck around 85-90% and then suddenly it goes up to 100%. (Without the optimized battery loading). I have to add, that the duration of the battery hasn’t changed, it is just the indicator and my capacity is 91%.

I‘ve already rebooted my phone a few times, made a few soft resets, tried to update the IOS 15 Update with iTunes, took off the lower battery modus and the optimized charging modus and also contacted the Service by calling them. Nothing helped. Wiping out all data is definitely the last step, which I try to avoid.

Would be great if someone has an idea what to do now. It’s such a shame that a very expensive phone has such bugs after ~14 months of using…