This circuit is a simple low battery level detector.
It can use for 3v to 15v batteries. when the battery voltage drop to low voltage LED be turn ON. you can change the low voltage that you want to detect it by VR1, as you see in following video, i set it for detect 11.9v because i want to use 12v battery, so when the voltage of battery is more than 11.9v the LED still turn OFF.
