I used to have a battery case and loved it. However, I didn't like the bulkiness of it as I put my phone in my pocket a lot. I now carry around a little powerstick. It is just about as awesome as the battery case, without the bulk. The downside is, it is another item to need to carry around. In my case, I just charge it a night with my phone, and then throw it in the glove box of my car. I also keep a cord and charger in the car at all times too. I rarely run out of power now.
There are tons of power sticks available. This is just one example:
http://www.amazon.com/Xtreme-88260-P.../dp/B00CZ5JCJS