New battery discharges from 50% completely and rapidly within minutes

I am having a strange problem after replacing the battery of my Huawei P10 (not Lite, Pro or Plus) (old battery was swollen and phone no longer turned on). With the new battery, the device itself works normally, but from 50% it discharges completely in less than 5 minutes and goes out (fake charge?). From 100% to 50% normal discharge (not amazing runtime, but acceptable for 50%, about 3-4 hours initially). I don't think it is a calibration problem because it didn't get better with multiple cycles. Over the course of about 10 days it got worse to 70% and is now at 90%. The cell phone then only starts with power supply by cable, shows 90% immediately after starting, then charges from 90 up to 100%, which takes about an hour. Then you can use it for a few minutes (maybe about half an hour at best) then it's back to 90% and turns off. You can use it continuously with the power cable connected, but it gets quite warm. So far I've only stressed that for a few hours at most. I've already tried a factory reset, but that didn't help. I thought about putting a new battery in again, but I was skeptical as to whether that would help since the battery was new. In other forums I discovered similar problems with the P10 Lite, but also once with a Samsung cell phone and the problem persisted after the battery was replaced (no solutions found, unfortunately). Can a defective charging board be the cause? Should I replace the board with the charging socket (as described here https://de.ifixit.com/Anleitung/Huawei+P...)? But the charging socket is apparently functional since the cell phone runs okay with a power cable. On the other hand, I suspect that such a defect may have already killed the old battery until it swelled up. Maybe the new battery will do the same soon if things continue like this? Any ideas?