Problems with powering on

I got my little sisters iphone 6s cause it suddenly one day wouldnt turn on. The phone is from 2018 so one of the last ones made.

I tried everything i could find online, but to no avail.

I had my friend come over with his old iphone 6 battery, we put it in and it worked,

it turned on fine and charged like it should, however, when we put the original battery back in, it still worked, hovering about 3-4% going up to 4 and then back to 1% power.

I bought a replacement battery and installed it and it worked fine, right from the get go, it charged fine and the phone would both turn on and off.

I just got home from weekend, i had turned off the phone with 97% power on friday and when i came back yesterday (sunday) it wouldnt respond to charging or any input, just like before i changed the battery.

is the charging port pcb bad or whats going on here?