I'm still using my 2 year old iPhone 5. I'm a fairly heavy user. The battery is on it's last leg. I charge at least 3 times a day or more. I go from 100% to 20% in 2? hours of constant use. It all depends on how much it has been used. Most get at least 2 years. Some get 4 or more. Just depends.
I have an iPhone 5 that my wife uses. She is a light user and can go all day with it. The phone is 3 years old and has lost some battery life but it is minimal. It is even eligible for a battery replacement, but since it has not been an issue my wife declined to get it done.
Had mine since it released and I have been a heavy user ever since. There is some drain to the battery that you can notice obviously, but it's not as bad as long as you know how to manage it. What kills my battery is anything that is constantly loading stuff from the internet. Such as Twitter. If I use Twitter for over an hour or two straight my battery will be really low.
Going forward I would love to keep using my 5s until I have to buy another battery and see how it runs.
I'm a moderate to heavy user. I keep my devices for two years and never had a problem with battery or anything else. I've had my 5S for 16 months it's perfect.
I've been using my 5 for 25 months. It's been in an Otterbox Defender most of the time. I took it out 3 times to clean the screens of debris. It looks brand new. Works great. It just needs a new battery. It is waning now as I'm a fairly heavy user. She's got until Friday. Then she gets traded for another with better curves.
I have used my 5S for almost a year and the battery life is still like a new, not sure what it will be after 2 years.
I use my iPhone for personal and business (lots of emails, notes, Twitter, FB, WA etc.). With Apple Watch the battery life has gone little better.
I bought my iPhone 5s in Dec. 2013, now the battery life still can last a whole day. The Low Power Mode that comes with iOS 9 will extend the battery life a lot.
I have had my iPhone 5s for two years now and have had no problems with the battery at all. It lasts all day into the night. I am a moderate to heavy user. It is one of my favorite things about my iPhone.
This is what I used and put it in my self real easy to do took like 10 - 15 min. Battery life is much better and does not phantom die randomly any more or go from 95% to 10% in five min time span.