Phone shuts off after back housing replacement

I recently replaced my back housing, and now my phone shuts off randomly. When it shuts off the screen turns whitish-gray with lines then goes back, and turns back on as if I rebooted it. The initial reboot appears(with the white screen and Apple sign). It stays on a little longer than one would usually expect. My phone stays on until I go into an app or play music then it shuts off and reboots again.

While replacing the new housing, I had to replace my battery. Could the battery I took from another iPhone 6 be defective. Please help, the constant shut off is annoying.