I have looked into a number of solutions to power 12v devices: Goal Zero battery packs (too expensive? $300+) 12v sealed lead acid battery with adapter (too dangerous? impractical to recharge? ≈$50) ...
I've used EveryTrail and was satisfied but am looking for something better... What are the features I should focus on for selecting an app? What bells and whistles are really useful on the trail?