Low battery indicator

This indicator will tell you in time that your battery is low. The main advantage of the proposed scheme is the accuracy of operation. In other words, the signal LED lights up immediately without a smooth increase in brightness. Plus, the device can accurately track the specified threshold.
The scheme is simple and, with proper assembly and working radio elements, it starts working immediately without configuration. You will only have to adjust the threshold of operation by the trimming resistor R2.
This circuit is designed for a 12-volt battery.
Also, the circuit can be remade for 6-to-4-volt batteries. To do this, you need resistors R1, R2 to take the resistance of 10 kΩ, and the resistor R4 - 560-100 ohms.
PS: You can build more than one circuit for a battery, but let's say three. That is, the first LED will operate at a voltage of, say, 11.The second at 10.5 volts, and the third at 10 volts. Thereby you will more fully possess information about the state of your battery.

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