I had one doing this same thing.
I replaced the charging port but when I plugged it in I got nothing.
The soldering looked fine under the microscope so I knew it had to be the battery or the board.
I did the battery connector reset several times until I got the screen to flash the back light.
Leaving it plugged into the original higher amp charger it would keep flashing the back light on and off.
Until it got enough power to boot the LCD. Then finally enough charge to keep the screen on.
Its a bad design on Samsungs part. The board doesnt allow the battery to charge enough before the battery can support the screen voltage draw. I think when the battery drains too much it can get to a point the board wont even charge due to this draw.