For the slow charging did you make sure your using a USB-c cable that can handle 45W charging, hopefully the one that came with the phone? If so then my only other guess would be that the phone is slowing it’s charging down because of overheating. Phones sometimes do this to make sure the battery doesn’t degrade from the heat if for some reason it gets hot while charging.
I’m not sure what could be going on for the battery problem. Did you check if the screen refresh rate is set to dynamic? Other than that it could just be you got a faulty model.
If I were you then I’d contact customer support and see if I can get it replaced or repaired under warranty.
