Stockae92, I've been to Mexico twice and Belize once since November for fishing and hunting trips. I didn't have any problem at all with flashlights and lithium batteries.
I had a couple of Pelican Cases with a dozen or so spare batteries in each (including one with CR123As) and they passed through fine.
Coming back to the USA, the customs inspectors were much more thorough and nosy. But, I didn't have any problems.
I checked all my lights and gear except for a Super Baby Pin (Mr. Bulk's light) which I carried on my person.
However, I had to get a supervisor in Houston to approve my 75 year old Ronson cigarette lighter for carryon. /ubbthreads/images/graemlins/icon8.gif
So, the advice about not taking anything you can't afford to lose is good. However, I wouldn't leave my Surefire behind for fear it would be taken by an official.
IMO, carrying topnotch personal lighting is a must for travel anywhere in Latin America.
Britt