20 - 30 minuten
Existing battery had become poor at retaining charge.
More or less OK. A simple jeweler's loupe or hand magnifier would be a useful addition, perhaps a combined hand magnifier and non-magnetic tweezers to hold the Philips #00 screws better.
Instructions to remove connector #6 (iPhone 3) and/or #7 (iPhone 3GS) were confusing. It should be made more clear that iPhone 3 only needs #6 removed, and iPhone 3GS needs both #6 and #7 removed, the other possible (and incorrect) interpretation is to remove only #7 for iPhone 3GS.
Removal of the old battery needed a lot of force with the spudger, and it bent a little, despite closely following the advice on iFixit, but did not damage anything else. The instructions about the glue strip (use the old one or remove it and peel/use the new one?) were unclear, but eventually became evident.
The tweezers I used (not included in the kit) to reassemble and place the screws were slightly magnetized and it was very difficult with all the screws as the screw stuck to the tweezers once in place. But it was practically impossible to place the screws without using the tweezers. Actually, magnetizing the supplied Phillips #00 screwdriver might have helped, as most of the screws could then have been placed using it rather than the tweezers.
The screw retaining the camera under the small metal strip was really fiddly, as both the screw and the strip stuck to the tweezers. However, all was finally completed successfully. The iPhone 3GS with the new battery is fully functional, and the new battery is retaining a flu charge as it should.