Make sure you have advanced task killer. I have an incredible and we used it with Lines in August- I just had to charge my phone every night.
My brother has an extended battery and yes, it does make it thicker but he says it is worth it so he can only need to charge every few days. I can't remember the brand of the battery, but it came with a new back cover that fit over the battery when he got it.
If the thickness matters to you, it might be worth just having two regular batteries, but then you have to swap them out to charge both. Have you looked into one of those emergency phone charger kits you get at drug stores where you use batteries? If you are only worried because of your trip it might be worth carrying around one of those.