Why is my iPhone XR new battery dying fast as the old battery?

I recently bought a iPhone XR battery to replace my old one because I was changing it 5 to 6 times a day,I replaced it with the battery I bought from here and it seems to be dying just as fast I do use my phone a lot but I’m confused why it’s dying so fast. I use power saving mode most of the time I get 3 hours of battery while gaming and while watching YouTube probably about 5 or 6 maybe not even that. I didn’t switch the the old BMS to the new battery cause I don’t know how to do that but if I needed to do that I feel like that should of been started on the description of the battery I bought from here. I need help it’s a brand new battery only 3 days old