20 - 30 minutos
Friends iPhone 3gs battery failed and they were bemoaning having to spend big bucks to replace it. Told them that we could fix it for a very small percentage of the cost of a new one and the agreed to try this.
Easy, easy, easy. The guide to installing the battery is excellent and complete. Took under 20 minutes start to finish. The friend is now SOLD on fixing stuff if it breaks as a first option.
Go SLOW when taking the old battery off the adhesive. A few seconds with a medium hair dryer helps alot. I use the little Pyrex Ramekin (sp?) small cups to hold the different parts. Each steps parts get a different container so no mixing and matching!