What might be killing the battery life on my rMBP?

Hey,

I was wondering if you might know what might be killing the battery life on my Retina Macbook. I have been getting about 4 hours or less on a charge, with brightness about 50 percent. I use it for a lot of web video watching, tweetbot, skitch, spotify, and writing stuff. Is something wrong? Are there any apps that I could install that would help me figure out the problem (if there is one).

Thanks.