A Simple Arduino Battery Tester

The Arduino battery tester is a simple tool that you can use to check how charged a battery is.

This project is perfect for anyone who wants to know roughly how much charge a battery has left before it runs out. It reads the battery’s voltage and lights an LED to give you a rough idea of whether a 1.5V cell is fresh, partly used, or flat. Rechargeable NiMH batteries sit at a lower voltage, so a fully charged one may show yellow.

This battery tester is a pretty barebones beginner Arduino project, but it can be extended to be a proper setup with proper casing and more. I go into detail at the end of the tutorial on how you could extend this project one step further.

A project like this one really showcases how you can make such a handy setup using the Arduino and a few pieces of equipment. It is also a great project for learning more about the basics of coding and electronics.

This battery tester isn’t super accurate and is probably best as a learning tool more than a precise measurement tool. I still highly recommend building this project as it is both fun and educational.

Equipment

The equipment that I use in this Arduino battery tester project is listed below. If you already have a starter kit, you should have most of the equipment, except the Zener diode.

Recommended

• Arduino Uno Amazon
• Green LED Amazon
• Yellow LED Amazon
• Red LED Amazon
• 5.1V Zener Diode Amazon
• 3x 100 ohm resistor Amazon
• 2.2k ohm resistor Amazon

Optional

• Breadboard Amazon
• Breadboard Wire Amazon

Video

If you want to see how to make this project, check out my video below. I go through all the steps required to get this cool battery tester project up and running.

You can find the full written tutorial on building this basic battery tester right underneath the video.

Assembling the Arduino Battery Tester Circuit

This battery tester circuit is pretty easy to assemble. If you have been following my Arduino tutorials, then you will notice we’re using a new component called the Zener diode.

The Zener diode is wired so current can only flow when the battery is connected the right way around. If you accidentally connect a battery backwards, the diode blocks it, protecting the Arduino’s analog pin.

The circuit does not protect against higher voltages, so only test batteries up to 5V, such as AA, AAA, C, and D cells.

The 2.2k ohm resistor limits how much current can flow into the Arduino’s analog pin if something goes wrong, such as accidentally connecting a higher-voltage battery.

The circuit also has three different LEDs; each of these LEDs represents roughly how much charge is left in the battery.

• Red will represent the battery being low/almost dead.
• Yellow will represent the battery being roughly half used up.
• Finally, green will represent the battery being full.

For each of the LEDs, we connect a 100-ohm resistor between the LED and the Arduino pin, so we don’t burn out the LEDs. This is very similar to what we did in the Arduino traffic light tutorial.

I will now quickly go through the steps of putting this circuit together. Underneath the instructions, you will find a circuit diagram if you find it easier to follow that.

1. Wire the ground pin on the Arduino to the ground rail on the breadboard.

2. On the breadboard, place the green, red, and yellow LEDs. Connect the ground pins to the ground rail.

3. Place a 100-ohm resistor onto the positive end of the LEDs, then hook a wire from a resistor to the relevant pins on the Arduino.

The following LEDs should connect to the relevant pin numbers.

• Red LED = 4
• Yellow LED = 3
• Green LED = 2

4. Now connect from analog pin 0 (A0) to the breadboard. After this, add a 2.2k resistor and the Zener diode, with the line on the Zener diode facing towards the Arduino. Finally, have a loose wire coming from the other end of the diode.

5. Finally, have a loose wire connected to the ground rail.

The code

The code for this Arduino battery tester project is straightforward, but I will explain each bit so you’re able to understand what we’re doing. If you just want the code and no explanations, then you can download it from our GitHub.

Firstly, we need to set up all our variables. This includes making sure the LED variables are all assigned to their relevant pin number mentioned earlier.

The analogValue variable is where we will be storing the value that comes from the analog input. We then do a calculation, which I will explain later, and store the resulting number into a variable called voltage.

Finally, ledDelay is how long you want the LEDs to remain on before switching off.

int greenLed = 2;
int yellowLed = 3;
int redLed = 4;

int analogValue = 0;
float voltage = 0;
int ledDelay = 1000;Copy

The setup function is called once and is the perfect place to set up all our pins. In this particular program, we only need to set up all our LED pins as outputs.

void setup()
{
  pinMode(greenLed, OUTPUT);
  pinMode(yellowLed, OUTPUT);
  pinMode(redLed, OUTPUT);
}Copy

Inside the loop function, we will do a couple of things. Firstly, we read the analog pin, which gives a value between 0 and 1023. To convert this to a voltage, we multiply it by 5.0 / 1023.0, giving a value between 0V and 5V.

void loop()
{
  analogValue = analogRead(A0);
  voltage = analogValue * (5.0 / 1023.0);Copy

In this last part, we compare our calculated voltage to our defined voltage values. Whenever the voltage falls between a set of values, we merely turn the relevant LED on. You can change the voltage variables to get the LEDs to display how you like.

  if (voltage >= 1.5)
    digitalWrite(greenLed, HIGH);
  else if (voltage > 1.2)
    digitalWrite(yellowLed, HIGH);
  else
    digitalWrite(redLed, HIGH); 
 
  delay(ledDelay);
  digitalWrite(redLed, LOW);
  digitalWrite(yellowLed, LOW); 
  digitalWrite(greenLed, LOW);
}Copy

Once you are done with the circuit, simply plug the Arduino into a computer and upload the code. Once this is done, we can continue onto testing and checking that it is working correctly.

Testing it all

When you first turn on and deploy the new code to the Arduino, you will notice that it keeps jumping between the LEDs. This is because the analog input wire is floating and picking up noise, causing our program to detect false positives.

To stop the jumping, you can simply ground the analog wire to the ground rail when not in use. You can also try grounding the other analog pins to help reduce the amount of noise it’s picking up.

To test it, hook up a battery to the two wires. Connect the ground wire to the negative end of the battery and the positive wire to the positive end.

The Arduino should pick up the voltage and tell the relevant LED to light up. If it doesn’t, then have a look at adding some debug lines for the battery input. You can use the Arduino serial monitor to set up some basic debugging. This should tell you if there is something wrong with reading the input or if there is simply a mistake in displaying the LEDs.

Extensions

Now, this tutorial just covers the very basics of setting up a battery tester using the Arduino. You can extend it to be a lot better and be more of a permanent device that you can use every day.

One improvement is to print the output to an LCD screen connected to the Arduino rather than using LEDs. This can give you more accurate information since we can write values to a screen.

You could also add a proper battery holder instead of using the two wires to check the life of the battery. This will probably make it a bit safer and make it look more like a professional battery tester unit.

A nice solid case would work well with a battery holder. Having the ability to 3D print one would be perfect for achieving this. Having a battery pack for the Arduino, so that it can be portable will make it perfect for anyone who needs to test batteries but isn’t near a power source.

I hope that you have been able to build this basic but cool Arduino battery tester. If you run into any issues or have anything else you would like to share, feel free to leave a comment below.