Honestly? I would get a 6 volt gel cell - rig yourself up a female USB with alligator clips and take a USB passthrough.
I did this just last weekend, and have been vaping on it all week to see how long it will last before I post the results just for fun. It still is not dead and vaping strong.
Just stop by any local batteries plus or radidilio smack or whatever, find one good for several AH - mine is 11 - make sure it's not gonna be TOO much extra weight for you - and head for the hills. They will be more than happy to give it a full charge for you too, so you should be able to forego the cost of a charging unit if you want until later. They aren't that bad though - 20 bucks will get you a good trickle charger.
So far this is day 8 - still working like a champ on 6 volt, 11Ah sealed battery, using a home-made battery box mod with cartomizers. I did put a resistor pack on mine to drop it down to 3.8 volts - I'm unsure about 6 volts on cartomizers so that part is up to you if you're a high voltage man or not.
Take care,
- Hap