battery level monitor

Battery Level Monitor Circuit

This simple battery level monitor circuit can indicate the charging process in 12 Volt Lead Acid battery or Tubular battery. The status of LED indicates whether the battery is accepting charge or not. It also indicates the full charge condition.

The battery monitor circuit can be incorporated in any battery charger like 6, 9, 12 volt etc. The only change needed is replacement of the Zener ZD with appropriate value. That is for 6 volt charger use 6.1 volt Zener and for 9 volt charger it should be 9.1 volt Zener.

Battery Level Monitor Circuit

battery level monitor

12V battery level monitor circuit schematic

The circuit is based on the switching of two NPN transistors (BC547) to drive the corresponding LED. Zener diode ZD is connected to the base of T1 so as to switch on T1 when the Zener conducts. This happens only when the battery voltage is above 12 volts. Green LED lights when the battery voltage is normal or battery attains full charge. Resistor R1 and Preset VR adjust the base bias of T1 for smooth switching. When T1 conducts, base of T2 will be pulled to ground and T2 turns off and Red LED extinguishes.

When is connected to the battery before charging the LED indications will be

  • If the battery voltage is above 12 volts (that is the normal terminal voltage of 13.8), Zener conducts and Green LED lights and Red LED remains off.
  • If the battery voltage is below 12 volts, Zener remains non conducting and Green LED remains off and Red LED lights.
  • When the battery is connected to the charger, and if the battery is accepting charge, Green LED goes off and Red LED remains on. When the battery attains full charge, Green LED lights and Red LED goes off.
  • If the battery is not accepting charge, Green LED never lights, even after the prolonged charging. This indicates that the battery is not attaining the normal terminal voltage above 12 volts.


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  • nidheesh

    Hello, anybody please help me to develop a simple system to monitor lead acid battery remotely.

  • Rahul

    Sir, I am working on Solar lamps for rural area as social activity. Lamp is made of 2 Watt SMD LED powered by 4 Volts 1 mah lead acid battery. I am using simple solar charging circuit for the same which is working fine. But it does not have battery full indicator etc. I am not from technical background so can not make it. Is it possible to have a low cost battery full indicator for the same?

    Thank You!

  • Faizan Hamayun

    I am here to have project related to Lithium ion 3.7-4.2V, 1100mAh rechargeable battery.
    I am in search of a circuit that can protect my battery from over charge,over discharge and should cut-off and shut down when fully charge.
    It should have fast flashing LED status for displaying short circuit or when the battery is dead.
    Slow flashing LED status while charge in process
    Solid LED when fully charged.
    Please reply.

  • junaid

    sir we will have to find the level of a battery which we are using as a source or another battery.

  • Surya

    VR 5K Should be adjusted to what value?

  • Abdul Khaliq Ansari

    i did this
    and i got working good, i did for 6V…
    but one problem in that, the red LED did not extinguish when the voltage reaches the desired value(say 6.1V)plz help me to solve this problemthanks in advance




    would you please tell me the changes for 4.2V battery. And how to calculate the values

  • kofi

    Can i use this circuit to battery in prepaid meter

  • jerry

    sir i use this circuit but not work,i use 12v 7ah battery.In VR 5K How it use?

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