This indicator will promptly inform you that your battery is low. The main advantage of the proposed scheme is the clarity of operation. In other words, signal Light-emitting diode lights up immediately without gradually increasing brightness. Plus, the device can quite accurately track the specified response threshold.
The circuit is simple and, with proper assembly and working radio elements, begins to work immediately without configuration. All you have to do is adjust the response threshold with trimming resistor R2.
This circuit is designed for a 12 volt battery.
The circuit can also be modified for batteries with a voltage of 6 - 4 volts. To do this, you need to take resistors R1, R2 with a resistance of 10 kOhm, and resistor R4 with a resistance of 560-100 Ohms.
PS: You can assemble more than one circuit for the battery, but say three. That is, the first Light-emitting diode will trigger at a voltage of, say, 11. The second at 10.5 volts, and the third at 10 volts. Thus, you will have more complete information about the condition of your battery.
