Replaced battery device will not turn on, Screen is good

My son's IPhone 5C was recharged 100%. The following day it was powered off and we couldn't' get the device to turn on, even after we tried recharging the battery. We replaced the battery, still will not turn on. We have a second IPhone 5C that had water damage and will not recharge the battery, I used this phone to test the battery and the screen to eliminate those two items as the issue. My son's screen works perfectly in the second test phone. Also, my son's phone is charging the new battery, I connected the new battery into the test iphone and it was charged. I'm at a loss, why won't his phone turn on? One other bit of info, he had a lifecase protecting the phone, so I don't believed the phone shut down due to damage.