I am probably about to replace the battery on my iPhone 6S. The battery charge drops like a rock, often being down to 10 or 20 percent by lunch time every day, with relatively light use in the morning. As best I can recall, this started around 7 or 8 months ago.
I have tried calibrating the battery, with no effect. However, I wonder if I am doing it correctly. I have found conflicting of information concerning this. All of the available information says to use the phone until it dies. After that, some guides say to let it charge up to 100% and you're done, some say to let it stay at 100% for at least two hours before unplugging it, some say that you have to do this cycle at least twice, and some say that you have to do a hard reset. I have tried calibration multiple times, using each of these methods, with no effect on how fast the indicated battery level drops. However, it is obviously not calibrated correctly. As I write this, my phone has been indicating zero percent battery, for 2 hours and 28 minutes, while playing a book in Voice Dream.
I will probably go ahead and replace the battery, as it is 4 years old, with 850 charge cycles on it, and occasionally has the battery related shutdowns. Therefore, replacement is probably advisable, but I am wondering if that is really what is causing the problem of the quickly dropping battery percentage. Other than this problem, I like the phone. I can't really afford a new phone right now and, even if I could, it would not be logical to spend at least $500 on a iPhone 8, which is the least expensive new iPhone, when I can spend $50 on a new battery.
Any advice on the right way to calibrate the battery or any other thoughts concerning the situation are welcome.