I am going to be purchasing (assuming I can find one) a Leupold Mark AR series scope. While I like the idea behind the "Firedot" reticule I've been stuck shooting a gun with a red dot who's battery has gone flat. It was not a fun experience. Since the reticule is battery powered, what does the reticule look like if the battery is dead or just not on? Is it simply a black reticule, or is it still useable?