Hi James, Did you do the repair yourself or through a repair shop? Either way its very possible that the ribbon cable could have been damaged or even melted when the screen was removed. First I would plug your charging into your ipad give it roughly 5 second and check to see if you have any sort of background light turn on. If you do its not your charging port. Also its possible that the ribbon cable connection was not seated properly on the logic board. If your charging cable still shows signs that it is charging your batter could be bad and may need to be replaced.
I hope that helps!
Best of luck,
Chris D