iPhone 4S with originally battery no longer charging. My assumption was the battery, which was not holding a charge well at all, had simply conked out after 5 years.
The first time that I did the repair it took longer than the guide said, which is no surprise since it was the first time. The second time that I did the repair it took less than 10 minutes. Why did I do it a second time? See below.
Before you discharge your new battery completely make sure that the new battery will actually take a charge. I did not do that, so when the battery finally dropped below 10% and I plugged it in, it was too late. The battery wouldn't charge, and my phone was dead again. Thus the second battery install. This time I powered the phone up and quickly took action to back up critical data. I did try to do an iCloud backup, via wifi, but the new battery did not have enough juice to make it through the entire process. The worst part about the mistake was having to buy a second battery and pay two shipping fees. And, BTW, the first battery that I was shipped had a fuller charge and maintained that charge significantly better than the second battery.