ive made about 4 low-battery indicator circuits, through-hole, and 2 using SMD parts, Green LED lights up and stays on when power is good and a red LED lights up when the power drops below the set level and the green LED goes out !
http://www.daftmike.com/2010/03/my-low-battery-indicator-circuit_22.html
very nice little circuit and using real easy and common components !
Oh btw, i used a much higher resistor for the LED’s so that they use less power when in operation !
hope this helps !