On the expanses of forums Reddit there were curious reports about a striking difference between the performance of the iPhone with different degree of deterioration of the battery. So, users of the iPhone 6S made measurements in the benchmark Geekbench before and after the replacement of the worn out battery, which turned out to be: 1466/2512 points before the replacement and 2526/4456 points after. Similar indicators were observed in some other cases and on different generations of the iPhone (before the iPhone 7, with which energy-efficient cores came).
Associate this with the problems of rebooting the iPhone 6S, which faced a small number of owners of this device. Then they were replaced as defective, but in iOS 10.2.1, Apple allegedly took steps to completely eliminate the incorrect voltage resulting in reboots. Reddit recommends checking the operating frequencies of the processor by the application CpuDasherX, and to get the full performance of the iPhone, you should replace the battery in case of great wear and tear.