Well, here are some ideas to that might help those facing the same problem. I can consistently charge the phone when it’s chilled, which is a confirmation of a problem with the battery temperature management. It’s either the temperature sensor/circuitry on the battery that is out of whack, or a charge controller which misinterprets the (correct) data from the sensor, possibly damaged in the process of opening the phone (heat damage). Either way, this can’t be helped easily.
For what it’s worth, the battery '''did not''' seem to be OEM, although the same format and appearance, the writing on it was all Chinese, while the original one was in English. There might be some incompatibility between the two.