Huffington Post: Whatever You Do, Don't Put iOS 8 On Your 4S

If you use an iPhone 4S, do NOT update it with iOS 8.

Apple says you can load your 4S with iOS 8, the new mobile operating system Apple released on Wednesday. But you really shouldn't.

iOS 8 was not made for us 4S users. It was designed for bigger screens than the 4S has. And that's the least of our worries. Ars Technica did some experimenting and found that iOS 8 slows the 4S down significantly. It takes an iPhone 4S 2.16 seconds to launch Safari in iOS 8, vs. 1.25 seconds in iOS 7.1.2. Launching the calendar takes 1.25 seconds with iOS 8 instead of 0.8 seconds in 7.1.2. Not cool.

I downloaded iOS 8 on my iPhone 4S (for science), and I can say from personal experience that it is murdering my battery. On Wednesday night my iPhone completely died from lack of battery life for the first time in years. I was using a battery case and charging it intermittently throughout the day, but it still didn't last from 7 A.M. to midnight.

http://www.huffingtonpost.com/2014/09/18/iphone-4s-ios-8_n_5842166.html