iPhone has bad battery drain and now it won't turn on

A couple of months ago, I plugged one of those lightning fans into my iPhone 6s (yes, I've heard of iPhones dying because of it, but I was silly and did it anyway). Anyway, a couple of days later, I really started to notice my battery would drain quickly, and my phone would heat up, as well as only certain chargers would work with my phone. This lead me to believe that I had ruined the battery, so I proceeded to order another battery for the phone. The battery worked for a couple of weeks, and then one day, the phone wouldn't turn on (forgot exactly what happened to cause this; maybe I let it die?). I got another battery, put that one in, and the iPhone would turn on for about 60 seconds (enough for me to unlock it and use it) and then it would just shut down. It wouldn't charge. After all this, I put the original battery back in, and it worked fine, albeit still with the bad capacity, heat, and only working with certain cables.

I got another phone, because the battery drain wasn't something I wanted to deal with, and just left the 6s unplugged for a couple of days. When I tried to turn it back on, there were no signs of life, and that's the state it's been in for a couple of weeks now. I've tried all the basic troubleshooting options: using an iPad usb wall outlet, taking the battery out entirely and just plugging it into the wall, using different cables, etc. I've done some research, and I'm thinking it's the charging ic. Please let me know what you all think; I have repaired several phones (screen + battery), and have some soldering/rework skills, so if that chip is the case, I am confident I can replace it, but I don't want to take risks I don't have to.

Thanks in advance!