They're a pretty cool add on to a AR carbine. I'm convinced that they must eat batteries while unused. Both a friend and I went through the starter batteries after a few range trips and 3-4 weeks in the gun safe. I pull my batteries when I get back from the range now.

You'll definitely go through the batteries faster with the brightness cranked all the way up. Good to have a few extras around. Like they say, if you're gonna stock up on canned tuna you'd better get a supply of mayonaise as well.