Here is the circuit diagram of low battery indicator from silicon chip electronics. This simple circuit lights LED1 when the battery voltage drops below the setting set by trimpot VR1. In effect, VR1 ...

The following circuit uses a low-power CMOS comparator and an LED to indicate low-battery voltage without causing excessive current drain. To view the application note, click on the URL below. Circuit ...

This circuit indicates the remaining battery life bAy varying the duty cycle and flash rate of an LED as the battery voltage decreases. In fact, the circuit actually indicates five battery conditions: ...