Other then pointing you to self fixit sites like www.ifixit.com there is not much anyone here could possible say as we did not witness your repair nor can anyone see the insides of your iPhone.
iPhones are not self repairable devices in Apple's view so you're pretty much on your own when you go down that path. And, since only Apple and their officially authorized repair providers have access to OEM new parts, whatever battery you purchases was most certainly not a true, new OEM replacement.