Had to replace the battery in my 3GS, phone was dying anytime it wasn't plugged into a charger, even if the battery said 100% it would die and I would have to put it on a charger to get it to turn back on
Was nervous that I would end up with a paperweight, but it went very smooth, I just followed the guide every step of the way, the only hiccup I had was that I do not own a hair dryer, so removing the old battery took longer than expected, that "mild" adhesive they have on there seemed like it could hold a car together lol, but I finally pried it out and everything else went perfect, the phone is acting like it did the day I first got it!
The tip about a magnet for the screws was an awesome idea! They are so small and I know I would have lost half of them if not for that tip! So thank you so much whoever thought of it, also use a hair dryer to loosen the glue holding the olds battery in, it took me about an extra 10 min. Just to get the old battery out, do it the easy way if you can