Why is my battery life so poor?

I was wondering if anyone else with the A1278 is having trouble with the battery? I am a college student (who can't afford a new laptop) and I would like to use my laptop to take notes in class, but even with the screen dimmed almost all the way and the wifi and bluetooth turned off, the battery can't even last through a 1 hour and 15 minute class. I can literally watch the battery percentage drop. The specs for the computer elsewhere on the internet state that it should be able to last for 5-6 hours at half brightness browsing the web, but I can't even get an hour out of it without having to plug it in because it died.

Any fixes or advice? I can't afford a new laptop at the moment.