@reafxxb0zhne7fj all of what you are mentioning sounds like a bad battery. Replacing it should resolve these issues. Since iFixit doesn't yet have a guide for that, use something like [https://www.youtube.com/watch?v=I8tEvp7paPg|this video] (right up to the 6 min mark) for that. Batteries are widely available at many online stores.
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.
Repair is War on Entropy!