Extending battery life

You can try running your battery down to 1% or even until the phone turns off like every single time.

ONLY IF YOU HAVE CWM (clockworkmod): go there, and reset battery stats.
Now you should plug your phone into the charger, and wait until it says 100%, and unplug it. If it still says 100%, you are good. If not, you have to plug it again, and here's the secret. Don't let the phone sleep. You can browse the net, play a game, etc, the key here is keep the phone awake while it is charging. The close you can get to 100% the longer you can use you phone without recharging.

Hope you find it useful!