Mostly Successful iPhone 3GS Battery Replacement
20 - 30 Minuten
My 3GS iPhone started shutting off without warning when the battery level reached around 15%. Then it started shutting off in the 20+% levels, then in the 40's, and eventually it would shut off in the 90's. Even if the battery was full, using the camera or the data network or internet intensive apps would kill the phone and shut it down. The battery indicator really didn't accurately reflect how much power was left in the battery either. I was going to upgrade to the 5, but with the disappointing 4S news, I decided to replace the battery to squeeze a little more life out of this model so I could hold out for the 5.
Mostly fine. I didn't expect the battery to be so hard to remove once I got to it, because it was glued to the phone. I also had a hard time finding the last screw to remove, because it had a sticker over it that said "do not remove." The hardest part was reconnecting everything. It wasn't too bad, but I had no idea how to reconnect tab 3. It's really hard to slide into the little slot, but you have to wiggle it in there before you lay tabs 1 and 2 down over it and connect them. If you don't connect 3 properly, your ear speaker won't work (though the speakerphone speaker will work). There was also some loose little piece of black plastic floating around in my phone, and I couldn't figure out where to put it, so I just left it out. That hasn't been a problem so far, so hopefully it was nonessential. :-/
All-in-all, it wasn't too bad, but I did have to put the phone together and take it apart again 3 or 4 times before I got it right. Luckily everything ended up working though, so that's all that matters.
See my notes about the repair. Be very careful with the connections and make sure you are meticulous about reconnecting everything, even if you have to make notes about how you disconnected them. Watch the video a couple times through before starting the operation. The video makes it look just a little easier than it actually is, but it's still totally manageable.