My iPhone 5 was losing its charge quickly. We've replaced many iPhones in my family because of battery and other problems. The iPhone 5 has all the capabilities that I need, so I'm now good to go for several more years.
Everything went fine. Almost lost a screw or two but found them okay.
Do the repair on a large table so that if you drop a screw it will be easy to find. Use the tray that comes with the battery to hold the screws.