Go out to your car and lay a screwdriver across the two battery terminals.
(please don't be stupid enough to do that) That is a 12v high capacity example of what happens when an atty shorts out on an unprotected battery. A protected battery can not exceed a specific amperage, it will simply create an open circuit instead.
Most of your newbie starter kits (510, eGo, and the like) have the protection built into the switch.
If you stick with AW batteries you won't have a problem
Trustfire's are also protected. in fact there are several choices of protected batteries.
BTW, not all AW batteries are protected, use high drain's at your own risk.