5 - 30 minuten
Verizon told me that the battery couldn't be replaced in the I-4 battery but I didn't want to change phones because my $200 Alivecor heart monitor was made to clamp onto that model. So I was happy to find a source for the battery, along with "how-to" instructions and a kit available containing all of the necessary tools (www.ifixit.com).
I replaced the battery at my desk and it only took a few minutes. In retrospect I should have taken a little longer and been better prepared because I lost one of the old screws (that I wasn't going to use anyway); more importantly, I forgot to clean the contacts as advised. Hopefully that won't cause any future difficulty.
I had two other minor issues: (1) My phone did not have the removable black antenna contact as shown in the video and I'm not sure what that should mean to me because the phone still works; and, (2) the battery connector didn't immediately fit into place but I remembered a previous user's advice about pre-shaping the flex cable and that helped me to immediately correct the problem.
I'm 70 years old and still handy around the house with a hammer, saw, paint brush and such, but when it comes to electronics repairs I'm 'all thumbs'. So, if I could do this I believe most anyone can. But, if I was to do it again I would prepare an area to work and follow the instructions a little more carefully.