I used to have a terrible battery life when on Stock rom KK. Now that I use a custom Rom 5.1.1, I can clearly see the difference: on stock, it would last one day, on custom it can last at least 3 days.
XDA Developers was founded by developers, for developers. It is now a valuable resource for people who want to make the most of their mobile devices, from customizing the look and feel to adding new functionality. Are you a developer?