My iPhone 3GS battery life got progressively worse over a period of months, crashing constantly at 50, 60, 70,80%, until eventually it would shut off still showing a 90% charge. I decided to try fixing it myself for $30 rather than spend $70 to ship it to Apple & be without my phone for a week.
Following both the iFixit repair guide and a few related YouTube videos that did a step-by-step repair, I had no serious problems replacing the battery & now have a working device that's as good as new. Also happy I opted for the iFixit kit instead of cheaper alternatives that seem to fail after a few charges. This one works great so far.
The guides aren't terribly clear on removing/replac