Originally Posted by zeker
I'm ordering an external battery pack.
Trent Battery Pack
Seems to me to be the best of both worlds. Phone stays slim, I can use conventional cases, and have more juice than an extended battery. I can also offer a bit of charge to others in a pinch. Just connect it once or twice during the day when not using the phone. They come in different capacities, some have two USB ports and can be used for both my phone and tablet.
I have something similar as well as a spare battery. It can very very useful and is not device specific. I lent it to a lady on the train once who was in a flap because her battery had run out and she needed to call someone. It was nice to be able to help her and she was very grateful.