5 - 30 minutos
The original iphone 4 battery was discharging too quickly
Using the Pentalobe screwdriver from the iphone liberation kit I was able to quickly open the iphone 4 case and using the plastic opening tools I got the old battery removed from the adhesive. The new battery was an exact drop-in replacement. The whole repair took a little over 10 minutes - easy fix.
Don't try to remove the old battery with the clear plastic tab that goes under the battery. It is easier to gently pry up the right side of the battery with the plastic opening tools, and then get your finger under the battery for the final removal.