After 3 years, his battery was becoming out of breath. We he was trying to do some efforts, like playing a game or surfing internet, he was fainting after less than 2 hours, needing external assistance to get resuscitate. His battery was over and needed a transplant.
To fix the problem, I order the iPhone 3GS Replacement Battery medical pack. Before starting the surgery, I read the guide 3 times, training in my head for the best practices. I started the operation by opening his front, I removed cable 1 and 2, no problem. A problem appears with cable 3, I unlock the plastic lever but I didn't understood how to get the cable off. After 10min, I decided to slide carefully on the cable, it came so easily ! The screen was off. I removed all electrical connections and screews so the main board could be free. I can now see the diseased battery. I fought against the glue for about 10 minutes taking care of the case. Now I just need to insert the new one. I replace the board and connexions. Before closing the body, I decided to blow on the screen to remove the dust. It was the worst thing to do : a big white stain appears on the screen. I was so sad. I decided to close the patient and wait. After 5 minutes, the stain has disappeared and I switch on the power botton. Every thing was okay but I was back in the past in 1970. After fixing the problem manually, he was like a newborn.
If it's your first time dismantling an iphone, it will probably take you about 1 hour to go through the guide. Take your time, that's not a race.