phone won't turn on after replacing battery

I was having problems with phone dying early, saying the battery was fully charged when it wasn't, and randomly shutting down. I opened my iPhone 6 and notice the battery had swollen up. I bought an ifixit battery kit for my iPhone 6 I installed it with no problems, but when I attempt to start it up the phone was unresponsive. I tried to start it while it was connected to a charger, but the phone remain unresponsive. I plugged in the old swollen battery and the iPhone would be stuck on the charging screen (the screen with the red battery whenever you're trying to start an iPhone from low charge).