iPhone bumb

Good day

I once fixed my iPhone 7 Plus screen, then I went to replace it , but when they replaced it they replaced it with an iPhone 8 Plus screen. So the screen didn’t close, then I went to enquire and they told me that the problem is the battery. I then got a battery replacement and indeed the battery was making a bumb on my phone, because it was old.

Now I got a battery replacement ,but after one week my phone has a bumb again with a new battery. So I’m not sure what is making a bumb on the phone