Phone dead after screen replacement

Hi, I recently broke the screen on my girlfriends phone and lucky had a whole other iPhone 6 display ready to go from my old phone. So I opened the broken phone up, took the screen half of the phone off and put the replacement in. Checked connections and went to power up phone to check lcd and nothing. No power, no vibrate when it would normal turn on or anything. I tried putting the old screen back on to see if it was just a probably with the replacement and still nothing. During this repair I forgot to disconnect the battery throughout the whole thing( though the phone was turned off) and I was wondering if maybe that fried the battery and it just needs replacing, or if this is an even bigger problem and the phone is bricked?