Powering Up Safely: A Guide to Wiring Lithium-Ion Batteries in Series

Introduction

Lithium-ion batteries are a popular choice for powering various electronic devices due to their high energy density and long lifespan. Wiring lithium-ion batteries in series is a common practice to increase overall voltage. In fact, every battery pack we sell consists of a collection of cells that have been wired in series (and often in parallel, too). In this guide, we'll walk you through the steps of safely wiring lithium-ion batteries in series to create a higher voltage battery pack for your projects.

Note that when connecting batteries in series you are increasing the voltage of the system. For example, connecting two of our 12-volt 100 amp-hour Renewed Power Packs in series will create a 24-volt 100 amp-hour battery. The overall capacity is driven by the lowest capacity in the string (the so-called "bucket effect"). So if you were to connect a 12v 50Ah battery in series with a 12v 100Ah battery, the result would be a 24v 50Ah battery. DO NOT CONNECT BATTERIES OF DIFFERENT CAPACITIES IN SERIES.

Safety First

Working with lithium-ion batteries requires careful attention to safety. Always use batteries from reputable manufacturers, and be aware of the specific requirements and limitations of the batteries you are using. Ensure your workspace is well-ventilated, and wear appropriate safety gear, including gloves and safety glasses. See our Safety page for more information.

An example of batteries connected in series. This is from YouTube user Michael Sewanaku. Link to video.

Materials Needed:

1. Lithium-ion batteries
2. Insulated wire
3. Battery holders or packs
4. Multimeter

If working with individual cells, you will also need:

1. Battery Management System (BMS)
2. Wiring or nickel strip
3. Soldering iron and solder and/or spot welder

Steps

1. Selecting Batteries:

   • Use lithium-ion batteries with the same capacity and voltage ratings.
   • For example, DO NOT connect one of our 12v 100Ah batteries in series with our 12v 20Ah battery.

2. Understanding Battery Orientation:

   • Identify the positive (+) and negative (-) terminals of each battery. Positive will typically be red and negative will be black.
   • Ensure proper alignment to prevent accidental short circuits.

3. Determining Voltage Requirements:

   • Calculate the total voltage needed for your application.
   • Ensure that the voltage does not exceed the maximum voltage rating of your devices.

4. Wiring in Series:

   • Connect the positive terminal of one battery to the negative terminal of the next.
   • Continue this series connection until you achieve the desired voltage.

5. Soldering Connections:

   • Use a soldering iron to secure the connections.
   • Apply solder evenly to ensure a strong and reliable bond.

6. Installing a Battery Management System (BMS):

   • A BMS helps monitor and balance individual cells, preventing overcharging or over-discharging.
   • Connect the BMS to each battery in the series according to the manufacturer's instructions.

7. Insulating Connections:

   • Slide heat shrink tubing over each soldered connection.
   • Use a heat gun to shrink the tubing, providing insulation and additional structural support.

8. Testing the Voltage:

   • Use a multimeter to measure the overall voltage of the series-connected batteries.
   • Ensure it matches your calculated total voltage.

9. Securing the Battery Pack:

   • Place the wired batteries in a secure battery holder or pack.
   • Ensure the pack is well-insulated and won't be subjected to physical stress.

Conclusion

Wiring lithium-ion batteries in series requires careful attention to detail and adherence to safety guidelines. Always refer to the specifications provided by the battery manufacturer and use a BMS to monitor and protect the battery pack. By following these steps, you can create a reliable and high-voltage power source for your electronic projects.

Sources

1. Battery University - "BU-304a: Safety Concerns with Li-ion" Battery University

2. Adafruit - "All About Batteries" Adafruit

3. PowerStream - "Series and Parallel Battery Configurations and Information" PowerStream

Note: Always consult the specific documentation and guidelines provided by the manufacturers of your batteries and components for the most accurate and up-to-date information.