This is another iteration of the Mophie Juice Pack charging problem...
I didn’t know if it was my iPhone 6S or my car (where I normally charge my phone) or a bad cable, etc. The problem is a bad solder in some circuit boards within the Mophie product:
https://m.youtube.com/watch?v=P7kZS_H1No0
It is technically fixable but I would just talk to Mophie. They are a decent company, and they should be able to replace a faulty product.
iPhone 6s, iOS 8.4.1, iOS 9.1