This should be in the Q&A, I Belive but to answer this question, a lot of things affect battery, first a old battery of course won't last you so long. Second are you running a custom Rom? And overclocking it with like CPU tuner or simmliar.
Are you running your brightness high,is your 4g on all the time, are you using music or social media a lot, playing games and so on.
That being said, moat customs roms can improve battery life to a degree, aswell as the kernel you use and what setting you are running it at, for instance I m running my custom Rom with underworld v8 no halvs sbc kernel
And my governer Set with ondemand at 769 max or something like that, I don't run 4g when I have WiFi, and my screen brightness is set low unless I need it brighter I will change it, I also have a lot of tweeks in my build prop, which a lot of other devs do aswell to help with battery life.
There is a nice section in these forums that explain governers you should read it, you will learn a lot.
I get about 2 days with normal use on my setup.
Hope this helps.