I have a problem with my iPhone 6 for over a month, I am desperate, please help me. The performance is decreasing as the battery level is lowering, but still at 100% it doesn't get the maximum performance (based on antutu and geekbench scores, and I can feel it in day to day usage). The CPU is never getting hot. I tried to replace my 3rd party battery with an original one one and it's better but not normal, I still get the same issue but not that worse. I think the battery is undervoltaged (at 10% 3.60mV - checked with Aida64 app, where my friend's 6 at 5% has 3.75mV) I don't have any Apple Stores near me and the iPhone is not under warranty anymore.