Lob0426 wrote:I think I would use a sealed lead acid battery as long as weight will not be a problem.
I'd like to point two things out: In summer, the pi might not want to sit behind 4" styrofoam. Heat is a common problem, cold is not. Just put the pi in the deep freeze and see if it keeps working: I bet it will.
About sealed lead acid batteries: They are not as "sealed" as one might think. They have valves, so in certain cases gas (oxygen and hydrogen) can escape the "sealed" battery. Therefore, it's strictly forbidden (and usually printed that way on the battery itself) to charge lead acid batteries in a gas-tight container. Also, lead acid batteries don't like the cold. If discharged, they can even freeze.