I'm wondering if there are any USB chargers available for canon DSLRs. I often head out for extended periods of time without electricity with my camera gear which always makes me nervous about when its going to run out. I've got something like this (a campfire charging stove) which produces at max about 10W of power. I'm wondering if there are any options for charging via USB? I'm using a 5D mkII/III.
If there aren't any USB based chargers around, what alternatives are there?