Something worth looking into is potential damage to the pins on the battery connector, not necessarily a smoking gun but something I’ve seen damaged on battery repair before. if it’s alright then I’d say the main culprit would be a chip on the board however I’m not 100% sure on this model of iPad, this doesn’t look like an issue with the battery replacement being subpar however; I’d expect that to show different symptoms like not holding charges well or boot looping (I would however say it is possible if the battery was more or less completely nonfunctional).