How to Use 18650 Li-ion Battery x 2: Examples, Pinouts, and Specs

The Samsung 18650 Li-ion Battery is a rechargeable lithium-ion cell widely used in portable electronics, power tools, and electric vehicles. Known for its high energy density, long cycle life, and reliability, this battery is a popular choice for applications requiring compact and efficient energy storage. When used in a configuration of two cells, the 18650 batteries can provide increased voltage or capacity, depending on the connection type (series or parallel).

• Power banks and portable chargers
• Flashlights and LED lighting
• Electric bicycles and scooters
• DIY electronics projects
• Robotics and IoT devices
• Uninterruptible Power Supplies (UPS)

Below are the key technical details for a single Samsung 18650 Li-ion battery. When using two batteries, the specifications will vary depending on the connection configuration.

The 18650 battery does not have traditional "pins" but instead features two terminals: a positive terminal and a negative terminal. Below is a description of these terminals.

1. Series Configuration: Connect the positive terminal of the first battery to the negative terminal of the second battery. This configuration increases the voltage (e.g., 3.7V + 3.7V = 7.4V) while maintaining the same capacity (e.g., 2600mAh).
2. Parallel Configuration: Connect the positive terminals of both batteries together and the negative terminals together. This configuration increases the capacity (e.g., 2600mAh + 2600mAh = 5200mAh) while maintaining the same voltage (3.7V).

• Battery Protection: Always use a Battery Management System (BMS) to prevent overcharging, over-discharging, and short circuits.
• Charging: Use a dedicated Li-ion battery charger with a constant current/constant voltage (CC/CV) charging profile.
• Balancing: When using multiple batteries, ensure they are balanced (same voltage and capacity) to avoid uneven discharge or damage.
• Polarity: Double-check the polarity before connecting the batteries to a circuit to avoid damage to the batteries or connected devices.
• Storage: Store the batteries in a cool, dry place at ~50% charge for long-term storage.

Below is an example of powering an Arduino UNO using two 18650 batteries in series (7.4V) with a voltage regulator.

• Connect the positive terminal of the battery pack to the input of a 5V voltage regulator (e.g., LM7805).
• Connect the output of the voltage regulator to the Arduino UNO's 5V pin.
• Connect the negative terminal of the battery pack to the Arduino's GND pin.

// Example code to blink an LED connected to pin 13 of the Arduino UNO
// Ensure the Arduino is powered by the 18650 battery pack via a voltage regulator

void setup() {
  pinMode(13, OUTPUT); // Set pin 13 as an output pin
}

void loop() {
  digitalWrite(13, HIGH); // Turn the LED on
  delay(1000);            // Wait for 1 second
  digitalWrite(13, LOW);  // Turn the LED off
  delay(1000);            // Wait for 1 second
}

1. Battery Overheating

   • Cause: Overcharging, over-discharging, or excessive current draw.
   • Solution: Use a BMS and ensure the load does not exceed the battery's maximum discharge current.

2. Uneven Discharge in Multiple Batteries

   • Cause: Batteries with different capacities or charge levels.
   • Solution: Use batteries of the same model and capacity, and balance them before use.

3. Battery Not Charging

   • Cause: Faulty charger or damaged battery.
   • Solution: Check the charger output voltage and replace the battery if necessary.

4. Short Circuit

   • Cause: Accidental connection of positive and negative terminals.
   • Solution: Use insulated battery holders and avoid exposing terminals.

1. Can I use 18650 batteries without a BMS?

   • It is not recommended. A BMS ensures safe operation by protecting against overcharging, over-discharging, and short circuits.

2. How do I know if my 18650 battery is fully charged?

   • A fully charged 18650 battery will have a voltage of approximately 4.2V.

3. Can I charge two 18650 batteries in parallel?

   • Yes, but ensure they are balanced and use a charger designed for parallel charging.

4. What is the lifespan of an 18650 battery?

   • Typically, 18650 batteries last for 300-500 charge cycles, depending on usage and care.

By following these guidelines and best practices, you can safely and effectively use Samsung 18650 Li-ion batteries in your projects.