Chosen Solution
I just replaced the battery on my iPhone 6. It is refusing to charge more than 8%. Does anyone know what might be causing the problem and how I could fix this? My phone is also heating up a lot, if that has anything to do with it.
could be Tristar failure. Seek out a qualified professional in your area who can diagnose battery, tristar, or install.
probably a sucky battery, and remember to replace the adhesive.