Battery Voltage monitor

All rechargeable battery has their specific level of charging and discharging, they are likely to get damage if the battery voltage exceeds that level. Here is a simple circuit battery voltage monitor used to indicate the state of battery by monitor them.

Circuit description of battery voltage monitor

The circuit of battery voltage monitor is fabricated and designed around op-amp IC LM709 configured as comparator. Where bi-color LED is used as indicator and indicates three voltage level state of a 12V battery. Resistor R1 with potentiometer VR1 is used as potential driver of voltage monitor circuit.

When voltage level rise above 13.5 volts, the output from IC1 goes low as a result LED begins to emit RED light. Similarly, when the voltage fall below a preset level (10Volts) the output goes high and the LED start to emit GREEN light. Resistors R3 and R4 is used as current limiter of LED.

battery tester

NOTE: Adjust VR1 such that LED begins to emit GREEN light when 10V DC is connected.


Resistors (all ¼-watt, ± 5% Carbon)

R1 = 1 KΩ

R2 = 18 KΩ

R3, R4 = 680 Ω

VR1 = 10 KΩ (Potentiometer)


IC1 = LM709

D1 = 1N4003


B1 = 12V Battery

LED = Bi-color LED

3 thoughts on “Battery Voltage monitor”

  1. Hi Krishan,
    This circuit looks very interesting. However, I need a circuit to monitor the status of a 6 cell Li-ion battery pack! So, is it possible to modify this to indicate the following status?

    At or over > 22.2v …. ….LED ….Green ON
    Between = 22v-18.5v…LED …..Yellow/Orange ON
    At or below < 18v………….LED…..Red ON

    What componets or values should I change to implement the above functions?
    LM 709 appears to obsolete,so can I substitute LM 208 or 308 op amps instead?

    1. I can suggest you to use zener diode circuit. Because the above circuit is unsafe and can stop working at any time. However zener diode circuit performs the best job and it is being mostly used in almost everything like chargers, Uninterrupted Supply etc.

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