Presuming your
battery is in reasonably good shape and charged, and you don't leave
lights on when you aren't using them, the
battery should be good for that. I have literally gone weeks without recharge, but am very frugal and use a small fluorescent
light for reading in bed.
For Mexico traveling tips, I suggest you do some reading in the appropriate forums of RV.NET where there should be a lot of info, and perhaps also at escapees.com.