Hi Welcome aboard.
I would suggest that you stay away from AA powered batteries, personally I find that the battery life is poor. The little Li Ion hold their charge well, last long and are small and cheap enough that you can take two or three. The camera will also be smaller in size.
Canon make a waterproof D20, my brother has one that he takes diving/snorkeling. It takes a NB-6L batteries and if you google for those, they are cheap enough.
My brother already had the Canon S95 and by coincidence the Canon D20 uses the same batteries.
I have to admit, I appreciate that you are hiking, but I would be tempted to take the G10 and a spare battery or two. Its already light and small for what it is and then maybe add the D20 or something similar as a back up.
here is some reviews
http://www.cameralabs.com/reviews/Canon_PowerShot_D20/