The power goes out after not long unplugging the charger

@akildoank this "after not long unplugging the charger" sounds very much like a bad battery. Since iFixit does not yet have a guide for that, use something like this video Replacement batteries are readily available. Do an online search to find a vendor that appeals to you.

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.