Why isn't my phone charging?

Dear community,

My iPhone7 Plus had a - or so I thought - faulty port. Prior I had noticed that I have to hold the charger in a rather odd angle to get the phone to charge at all. At some point, the battery ran out and the phone hasn’t switched back on ever since. Occasionally, it showed the “red battery” (minus or with the lightning cable) on the screen, yet, never charged to the point where it would switch back on. Hence, I went ahead and replaced the port. I had previously successfully replaced the battery and also added a new “water-resistant“ seal.

While I am no expert by any means, I was careful and everything appeared to have gone smoothly (no screws left over, didn’t tighten screws overly tight, used nitrile gloves and was overall careful). The phone, however, won’t charge, let alone switch on. It won’t even show the aforementioned “red battery” anymore. So far, ifixit has kindly sent me yet another replacement for the port but the issues persist. The very least I would have expected was that I would get the “red battery“.

I was wondering what the underlying cause could be? Did the logic board take damage somehow? Is the battery overly drained that it simply won’t react anymore? Is it worth getting an iPhone 7 plus-appropriate DC power cable to bypass the battery to see if the phone will at least switch on? May a battery (re)activation board be useful?

Many thanks for your input.

Happy New Year,

Georg