After battery replacement phone won't power up- I may have goofed?!?

Hi- I purchased an iPhone 6 Plus battery from ifixit, with tools and did the replacement today. I followed the instructions on YouTube from ifixit. After putting the new battery in I started up the phone before closing the thing up to see that everything was working- and it looked like it did! Apple logo- then lock screen. Looks good! Then I go to turn it off - oh no - the touch screen doesn't work! The touch screen connector wasn't connected!!! Because of that, I had no way to turn off the phone. So I unplugged the battery connector (probably a bad idea?) to power down, then I opened back up the connector cover to connect the touch screen clasp (which was not connected at all)- put that all back together, and then reconnected the battery clasp and cover, and this is when the phone would not power up.

Some additional details:

- phone worked fine before this

- the new battery registered a 52% battery charge when the phone was briefly on

- I connected the battery being replaced to check - it had 80% charge right before being replaced- still didn't work.

- I tried iTunes thing (connecting to computer via an apple usb cable) still nothing.

- the screen and battery connectors all look good- there doesn't seem to be any damage.

My questions:

- Did unplugging the battery connector while it was on 'fry' my phone?

- Did the touch screen connector being loose/unconnected cause my phone to be fried?

- was it a combination of the previous 2?

I just need to know if this phone is a lost cause.

Any information here is greatly appreciated.