My wife's iPhone 5S would simply shutdown while processing... anything. It happened haphazardly and at very inconvenient times. The battery usage would show at 100%, and suddenly it just went out of power. She's had the phone about 21 months. I figured it's about time for a new battery.
This repair was very straight-forward and quick. Battery removed was actually easier this time around than when I did the same for my daughters phone. I didn't actually have to remove the adhesive strips.
Just take your time, be careful with the connectors, don't forget to put all of the shields back on.