10 - 30 minuten
My battery on my 4s would usually be down to 10% by noon. The battery is 1 year old. If not for my Mophie I'd been in real trouble. I tried turning off notifications, location srvcs, wifi, etc. I live in what they call a fringe area as a Verizon customer. I installed a Verizon network extender and that helped my signal at home. I did notice that once I was in a strong signal area the battery lasted longer. Two days after installation I've noticed a 30% improvement in battery time. I suspect apps, weak signal, are all playing a part in addition to I use the cr%# out of my phone.
Repair went beautifully, I watched the iPhone 4 video, in addition to following the iPhone 4s written instructions. My battery had extra adhesive on it and using the plastic prying tool, I kept light pressure on lifting the battery out for nearly a full minute before it began to slowly lift out. The antennae popped out unexpectedly but it didn't go far. Putting in new battery went without any problems.
I'm not sure where I got the advice, but I used a large size shoebox lid from a pair of my wife's shoes to do the repair inside of. Good thing too, as the antennae popped out unexpectedly, and one screw popped out of the tweezers but with the shoe lid all was contained. And be very patient on lifting the battery out, don't even bother with the plastic tab. Oh, and a video of the battery replacement on a 4s would be nice. There is an extra screw on the 4s and the antennae is a little different.