The client who had called me had complained of how after 2.5 years of operation, his phone was not sustaining battery life throughout the day. After checking some iOS settings and ensuring he wasn't running a bunch of apps/services all at once, I proceeded to order a battery.
The repair went great now that I look back, but it's a process for sure. Thank goodness I had a heat station and some other tech tools at my disposal. Prying the battery off without having a heat gun can easily bend the aluminum casing. I have some fine tips which allow for precision heating, so things went a little easier after that. After installation, there were white bars on the top and bottom of the screen and lines in the middle of it. This defect soon worked itself out, but do make sure that all cables are correctly seated in the phone when putting back together.
BE AWARE OF STATIC ELECTRICITY! WEAR YOUR ESD-WRAP! I work with latex gloves, but on the initial replacement I did not wear them. Be aware that ESD is a real problem that can cause adverse effects during repairs. Always wear a pair of rubber gloves or a wrist wrap during repair and ensure that you're grounded. The repair came out just fine after that.