10 - 30 minuten
Accu was almost dead. My 14 year old daughter hears i-phone music 49 hours a day and the 4s was never a great thing for power.
The repair was Kids Play. I'm an electronics man so it was especially easy for me, but anyone who hasn't got three left Hands and just a little feel for the real world could do it. Two screws to remove the case (just a Little care, Keep the force used compareable to the Job) Two screws for the barrery plug (same here) and remove with care. Same for the accu, which is retained with some sticky stuff but can be removed without Trouble. Just don't use a crowbar or sledgehammer. Replace in reverse order, use minimum force as before. Done.
First of all the (excuse me) crap spread about the i-phone being glued together, second the good instructions and third, don't believe all that you hear, especially from Apple.
Be careful with the battery plug, it is really sensitive to force, and keep it clean. Otherwise just don't be frightend to touch the thing, it won't bite. The advice about cleaning with alcohol, be careful there. Most available cleaning alcohol can contain up to 10% or more water. Use MEK 99% if you can get it, otherwise better not to touch the electrics or use clean fine gloves. I just made sure not to touch plug or wires with the naked hand. Good work, Ifixit :-)
Sorry for no photo, I took a Video at the repair but got interrupted. Switched it off and forgot to turn it on again.