20 - 30 minutos
My iphone 3GS is almost 3 years old and for the past few months, it would shut down at about 60% battery life. I was super frustrated so I searched online. I found ifixit, watched the tutorial, read the reviews, and decided to order a replacement battery and tools. I figured $40 was cheap to get my 3GS working.
It took me about 45 minutes but I was able to install the new battery and reassemble my phone. And my phone works great now! No more shutting down at 60% and it lasts the whole day!
I would pay close attention to the connectors before disconnecting (take mental or actual picture). Also, pay attention to the screw next to the camera since there is a small metal piece attached to it.
The best advice in another review is, generally "pull harder and push harder than you think is ok." This helped me a lot in reconnecting the tiny connectors.
Thanks ifixit!!!! I would highly recommend this product and instructions for the iphone 3GS battery replacement.