Low Battery Light?

Anyone know of a simple circuit to turn on a light when a battery starts getting low?

Use a comparator and a zener diode.

Except I'd use an LM311 instead of the LM339 as it can drive the LED more brightly.

**broken link removed**
https://www.elecfree.com/electronic/low-voltage-battery-monitor-by-lm339/

I have used the LM10 adjustable accurate voltage reference and opamp in an 8-pins case. It works with a supply as low as 1.1V and as high as 40V.

Hi, see the attached, the pot is 100K if you want a led lit when bat ok keep top led and resistor and remove the bottom, if you want the led lit when bat below set point remove top led and resistor.

The zenor should be as close to half the voltage you wnat to monitor.

Unlike the above suggestion, it wont work below 3-4v