AA Travel chargers only charge AA's and AAA's they are cheaper to make. How well they charge batteries depends on a large list of factors. Faster chargers use higher charging currents which in turn charge your batteries much faster but and this is a ...
You can take chargers on planes I've done it before!!
My bet is that the original batteries are/were 6V's. I'd try to replace them with something very close to the original type. Golf cart batts. (which is what you've got, yes?) are usually 6V and are much better at high current & deep discharge compare...