A family friend had an iPhone 6 with a battery that would die very, very fast. So they came to me and asked if I could do it, and I said yes.
The repair went very smoothly. I have done this multiple times before and only had one minor issue. It was all completed in under an hour.
The one issue I had was when removing one of the battery strips, it broke. Luckily I was able to grab it with a pair of tweezers, since I had just started pulling on it. So be careful and take your time.