20 - 30 minutos
My iPhone 3GS started to shut down everytime I used any app for more than 20 seconds, even when the battery was nearly full. Battery was messed up.
I saw this DYI kit and gave it a go, and now, I'm incredibly grateful I did!
The repair took 45 minutes. I followed the step by step tutorial and had no troubles at all! The inside of the phone is neatly numbered and organised.
The only "hard" part, was removing the old battery. It is glued to the backcase, so you'll need more than the spudger to remove it.
I tried using a hairdryer to warm the glue, and ended up removing it without any difficulties.