My wife was complaining about her iphone 4s had to be charged too often. Ordered a new battery from iFixIt. Next day the iPhone's battery went dead. Charging would not even wake it up.
I've replaced one other 4s battery before, so I studied iFixit's pictures and video's and felt confident in replacing batteries on 4s phones. On the first repair I spent little longer ( 30min ) so I could understand what I was doing.
On my wife's phone, I think it took less than 12min. After the replacing the battery and turning it on the phone came on and the new battery showed 50% charge. I discharged the battery down to 10% then charged it overnight. The phone works like new again.
First time 4s battery replacement watch iFixit's video then look at step by step pictures.
Be sure the phone is powered off before starting. I used a magnifying glass.
Keep track of the small screws. Don't mix them up.
The 4s phone is an easy phone to take apart and replace the battery.
The kit comes with the tools you need. A small tweezer may be handy.