I used to use the usual lead-acid or marine grade batteries, but they were pretty heavy. I'm sure the LiPo batteries are much lighter as well.
Though, I'd recommend getting one of these
http://www.amazon.com/dp/B00DVB7F0S?psc=1.
And plop that in one of those Plano boxes.
This is pretty much what I have. It's a 15Ah battery, that's very small and lightweight. Lasts multiple days as well. Drilled a hole for the cable output, and gooped it for a watertight seal.