Tablet refusing to charge, suspecting broken battery / charging port.

The story for anyone interested, skip to the bottom for the problem:

So I have had this Tab 3 for a REALLY long while now, it used to be completely fine, ran for ~2-3 years when I bought it in ~2014, and then started having battery issues. In 2015 the battery completely died and it sat in the cabinet for a couple of years, ~2018 came around and I bought a replacement battery and USB connector, replaced them, took it on a trip, fully charged it, and by the end of the day the battery ran out, it died, never to turn back on again, didn’t respond to chargers.

Today I managed to get it to come back to life by plugging/unplugging the battery in and out, and using every button combination on the internet to get it to power on, after a few hours of trickle charging and plugging in/out, it did, and was even at 30% charge. I used it for a couple of hours, updating and deleting apps, and put in to charge, it got to 50%, I then unplugged it to further pick some apps to download and when I tried to plug it back in… Nothing, no longer responding to any cables.

Story time over.

The problem-

So the issue I have right now- the tablet is refusing to charge from a powerbank/wall adapters/USB port, tried with a million different cables and adapters, none worked at all, the PC also wouldn’t detect it when connected via USB, it slowly died while I tried completely resetting it and turning it on/off again, and is now again in a fully dead state.

I’m suspecting the connector might be bad, but it was literally used a total of 6 times since I replaced it, it’s essentially brand new, and it stopped working after 1 un-plug and plug in, in a 30 second window, nothing at all happened in between that last unplug and the next plug in.

I’m out of idea’s at this point, a replacement battery(20$)/connector(5$) would literally cost more than the value of a new one, but I’d really like to, if possible, repair it, as it’s an excellent movie display when travelling. Any suggestions?