I have a 6 X 2V (400Ah) batteries in the office and I use usual DC to AC inverter to run our computers. One problem that we have is there is no way to know how soon our batteries are going to die. I got usual volt meter, but I need to monitor that all the time. What can I do to make a beep when a battery volts goes below 11.5? I think it is very simple thing but I don't know what it is called or how to make it.


Here is a circuit I made some time back and it was very useful. The Zener value can be roughly between 7v and 10v. The 555 IC acts as a comparator and turns on the output at pin 3 (OUTPUT) when pin 2(TRIGGER) is less than 1/3 Vcc. Adjust the Potentiometer(R1) so that the output is turned on at 11.5 volt.


simulate this circuit – Schematic created using CircuitLab

A quick search returned a few circuits that may be better. I had originally built my circuit based on the second link.



For the second one, you can replace the LED with a buzzer.

For all circuits, select a buzzer that works when directly connected to a voltage (ie: make sure it is not a simple piezo disk or speaker).

  • \$\begingroup\$ Answers that depend almost completely on links are discouraged on Stack Exchange. Links go bad or change all the time on the web. The result is that in the future this answer could become useless. You can improve your answer a whole lot by publishing a picture of a suitable circuit. As a matter of fact this site even has a built in schematic drawing tool that could be used to show a low battery buzzer circuit. \$\endgroup\$ – Michael Karas Dec 11 '15 at 11:52
  • \$\begingroup\$ Thanks for the feedback. I've edited the answer to add a circuit. The built in drawing tool is pretty easy to use. \$\endgroup\$ – Vinod Dec 15 '15 at 13:00
  • \$\begingroup\$ @Vinod I am not able to simulate the schema above, could you please help me to make it work? I also looked at the second link and I can't understand it. It says Battery + and - but hard to figure out where is the battery. I appreciate your help! \$\endgroup\$ – Dilshod Dec 24 '15 at 11:05

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