Macbook Pro Battery Drainage?

Hi! I have a late 2011 13" macbook pro. I am currently running the latest version of Mountain Lion. For a while now, my battery life has been awful. I am getting at most only 2 hours of battery life with light usage, screen dimmed to only 3 or 4 notches up from black, no backlit keyboard on, bluetooth disabled. Just typing this was enough to drain another 4 percentage points. Why is it so awful? What can I do to help this?