This is the design of battery level indicator circuit. This circuit is designed for 9V battery operation, as this circuit will start dimming below 7V and will be completely turned off at 6V. If you want the LED indicator not to dimming but just abruptly turn off at below 6V, then you can remove R3, and change R1 to 330k. This is the figure of the circuit;
[Circuit diagram source: National Semiconductor Application Note]
