First of all you should check if your battery is going into deep sleep mode. You can do that by installing
Bettery Battery Stats, and leaving your phone idle with the screen off for some time. You should read the forum post to understand how it works. If after leaving your phone on "stand-by" you realize that it's not going into Deep Sleep mode, then you should find out what is keeping your phone awake.
I used to have the same situation as you, and it turned out that I had set the WiFi Sleep Policy in Viber to override the Roms setting, and consequently leaving my WiFi always on (which prevents your phone from sleeping). After fixing the issue in Viber my phone now turns WiFi off after 15 minutes of leaving my phone idle.
Now unless your battery is actually dying on you, I'm sure you can get a better battery life. I am using Tasker to program my phone to turn WiFi off when I turn off my screen, and then turn it on for 1 minute every 15 minutes during the day, and at nights it does the same thing but with an interval of 1 hour and half. There are apps in the Play Store that do this too, I've tried these both, and they work as they should, and they can even control your Data connection
Green power
Deep Sleep Battery Saver
All in all I've been losing an average of 1.7% during the day, and 0.7% and 1.2% per night. My battery currently lasts about 2 days on one charge. This is all assuming it is actually your WiFi that's preventing your phone from sleeping, I just figured I'd share my experience in case it is in fact that; the important thing being that you could probably get the same results as I have (or even better, considering your battery isn't busted) if your phone is actually going into Deep Sleep.
