Did you use the custom adhesive or the 3M double sided tape?
Flashing red light could mean that your battery is not being detected. It is possible that you did not sit the battery connector properly. Hopefully the connector was not damaged when reinstalled. It is small and can be a little fiddly. I had to remove the battery when changing out the screen. After replacing everything, the same thing happened. I figured out the problem when the phone went from empty to full each time I pressed top third of the back cover plate.