In this guide, we’ll show you exactly how to use two 18650 lithium-ion batteries to safely power an Arduino Uno, using a simple setup with visual demonstration.

Why Use 18650 Batteries for Arduino?

18650 batteries are rechargeable, high-capacity (often 6800mAh or more), and deliver a nominal voltage of 3.7V. When used in series, two 18650s provide approximately 7.4V — perfect for powering an Arduino board through its VIN pin.

What You’ll Need

  • 2 × 18650 3.7V lithium-ion batteries (e.g., 6800mAh)
  • 18650 battery holder (2-slot)
  • Arduino Uno (or compatible board)
  • Breadboard (optional)
  • Jumper wires (optional)
  • LED and 220Ω resistor (for test circuit, optional)

Wiring Diagram and Setup

 

In your setup:

  1. Insert the two 18650 batteries into the holder.
  2. Connect:
    • Red wire (positive) from the battery holder to the VIN pin on the Arduino.
    • Black wire (negative) from the battery holder to the GND pin on the Arduino.
  3. The Arduino will now receive around 7.4V and regulate it internally to 5V.
  4. (Optional) Test with an LED connected on a breadboard to pin 13 or any digital pin.

As shown in the image above, this setup powers the Arduino and lights up a green LED connected to a breadboard.

Important Safety Tips

  • Always use a battery holder — never solder directly onto 18650 batteries.
  • Ensure the batteries are connected in series, not parallel.
  • Avoid overcharging or over-discharging — use protected 18650 batteries if possible.
  • Do not connect the batteries directly to the 5V pin — it bypasses the onboard voltage regulator and could damage your Arduino.

Advantages of Using 18650 Batteries

  • High capacity for long-lasting power
  • Rechargeable and reusable
  • Ideal for outdoor, wireless, or robotic Arduino projects

Conclusion

Powering your Arduino with 18650 batteries is a simple, effective way to make your projects mobile and energy efficient. With just two 18650 cells and a basic holder, you can achieve a clean, reliable power supply anywhere.