@johnrett this could be a battery issue as well as a charging board issue. For now, I would suggest that you start with the battery (do consider the charging board since you have the phone disassembled already) Also, check the ribbon cable from the charging board to the main board for any damage.
Since iFixit does not yet have specific guides for this, use the ones from here Those have been written in Spanish. Use a browser that will do the translating for you, if needed.
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 a device with the same issues 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!
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