Is is a software issue or hardware issue?

[Android Central Question]

So late last year my S8+ had a serious failure. I updated to the latest Android software at the time and noticed some weird issues start, like battery drain and it not being quite as responsive. Other than that, it was working normally. One day I tried plugging it in to the charger and it wouldn't charge. I kept trying to charge it (plugging and unplugging the charger from the phone). The phone suddenly started getting warm to the touch, especially on the back of the phone. Then the battery went from 50% battery to less than 20%, and eventually failed to turn on at all, regardless if it was on the charger. I took it to a repair shop to have the battery replaced, and though the phone turned on and seemed to work properly for the shop, it went right back to the same state shortly after I got in the car. I drove home to see if maybe wireless charging would help it out and nothing seemed to work.

Fast forward to today (I've since picked up a Note 9). I ordered a new battery and replaced it myself in the hopes I could at least sell my S8+ or let my wife use it for work. It turned on and got to the "Android is starting" splash screen then turned off. Put it on the wireless charger and nothing, then plugged it in to the phone directly and it turned on. It got to the Android setup screen and then turned off again. It shows that it's charging but doesn't stay on long enough for us to get through set up. Do you think this is a issue with the version of Android on the phone or did I fry something when plugging and unplugging the charger?