Chosen Solution
My iphone 6s recently started doing this. It only works when plugged into the charger and when unplugged it turns off shortly afterwards . I’m thinking it’s something to do with the battery but I’m not exactly smart enough to know any of this yet. My phone has had water damage and has been repaired for a broken screen. The screen is also a little glitchy like it looks like stripes of color from the image appearing. Help plz.
If the logic board has been cleaned properly from liquid damage repair then the screen and battery needs to be replaced. I have linked guides and where to buy the part from iFixit: iPhone 6s Screen Replacement iPhone 6s Screen iPhone 6s Battery Replacement iPhone 6s Battery
