A Guide to BMS Connection

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In the world of battery management systems (BMS), proper connections are crucial for efficient and safe operation. In this article, we will dive into the types of BMS connections, understand the different types of connection diagrams, and also answer some common connection questions and solutions.

Understanding BMS Connection Types

BMS connections can be broadly classified into two main categories: parallel and serial. Each connection type offers unique advantages and is suitable for different applications. Let’s explore each type in detail, along with their subcategories.

Parallel Connection

In a parallel connection, multiple batteries or battery packs are connected in parallel, with their positive terminals linked together and their negative terminals connected. BMS parallel connection has the following advantages:

Increased capacityParallel connections allow you to combine the capacities of individual batteries, resulting in a higher overall capacity
Longer runtimeWith increased capacity, your battery system can operate for extended periods before requiring a recharge
Load sharingThe load is distributed evenly among the connected batteries, ensuring efficient power delivery
RedundancyIf one battery fails, the remaining batteries can continue to power the system, providing increased reliability

Serial Connection

In a serial connection, multiple batteries or battery packs are connected in a series, with the positive terminal of one battery linked to the negative terminal of the next. The following are the advantages of BMS serial connection:

Higher voltageSerial connections combine the voltages of individual batteries, enabling higher operating voltages for specific applications.
Consistent voltageAs the batteries discharge, the voltage remains relatively constant until the pack is depleted.
Compact designSerial connections often result in a more compact overall battery pack design

It’s important to note that while parallel connections increase capacity, they do not increase the voltage output. Conversely, serial connections raise the voltage but do not affect the overall capacity. In some cases, a combination of serial and parallel connections (serial-parallel) may be necessary to achieve the desired voltage and capacity requirements.

When designing or implementing a BMS connection, it’s essential to consult with experts or refer to manufacturer guidelines to ensure proper configuration, wiring, and safety considerations are met. Improper connections can lead to hazardous situations, reduced battery life, or system malfunctions.

2s vs 3s BMS Connection

Above we talked about two types of BMS connection, in this part we will explain the 2s BMS connection and 3s BMS connection in the battery pack series connection. 2s and 3s refer to the number of cells connected in series in the battery pack.

2s BMS Connection

A 2S BMS connection involves connecting two battery cells in series. In this configuration, the positive terminal of one cell is connected to the negative terminal of the other cell, effectively doubling the voltage output while maintaining the same capacity as a single cell.

2s BMS Connection

Key points about 2S BMS connections:

  • Suitable for applications requiring higher voltage than a single cell can provide
  • Voltage output is approximately double that of a single cell (e.g., 7.4V for two 3.7V lithium-ion cells)
  • Capacity remains the same as a single-cell
  • Requires a BMS capable of monitoring and balancing two cells in series
  • Proper cell matching and balancing are essential for optimal performance and safety

3s BMS Connection

A 3S BMS connection takes the series connection one step further by connecting three battery cells in series. This configuration triples the voltage output compared to a single cell while maintaining the same capacity.

3s BMS Connection

Key points about 3S BMS connections:

  • Suitable for applications requiring even higher voltage than a 2S configuration
  • Voltage output is approximately triple that of a single cell (e.g., 11.1V for three 3.7V lithium-ion cells)
  • Capacity remains the same as a single-cell
  • Requires a BMS capable of monitoring and balancing three cells in a series
  • Cell matching and balancing become more critical to prevent imbalances and ensure safety

How to Choose?

Choosing between a 2S or 3S BMS connection depends on your application’s voltage requirements and your BMS’s capabilities. Higher voltage configurations may require additional safety measures, such as overcurrent protection and thermal management, to ensure safe operation.

Following the manufacturer’s guidelines and diagrams is crucial when implementing 2S or 3S BMS connections. Proper wiring, cell matching, and balancing are essential to maximize performance and prevent potential hazards.

Additionally, some applications may require even higher voltages, necessitating configurations beyond 3S, such as 4S, 5S, or more. In these cases, it’s essential to consult with experts and adhere to industry standards and best practices to ensure the safe and efficient operation of your battery system.

Factors to Consider and Troubleshooting

While following diagrams and guidelines is essential, there are additional best practices and troubleshooting tips to keep in mind for successful BMS connections.

Factors to Consider Before Connecting

  • Double-check all connections before powering on the system.
  • Use appropriate wire gauges and connectors to minimize resistance and ensure secure connections.
  • Implement redundant safety features, such as fuses and circuit breakers, for added protection.
  • Regularly inspect and maintain connections to prevent corrosion or loosening over time.


  • If you encounter issues, systematically check each connection point for loose wires, incorrect polarities, or damage.
  • Consult the BMS manufacturer’s documentation or seek professional assistance if problems persist.
  • Keep detailed records of your connections and any modifications made for easier troubleshooting.


Mastering BMS connections is a crucial step in unlocking the full potential of your battery management systems. By understanding connection types, following detailed diagrams, and implementing best practices, you can ensure the efficient and safe operation of your battery packs. Remember, proper BMS connections are not just about functionality; they also contribute to prolonged battery life and overall system reliability.

If you’re still unsure about any aspect of BMS connections or require professional assistance, don’t hesitate to reach out to MOKOEnergy. Our knowledgeable team is ready to guide you through the process, ensuring that your battery systems are properly connected and optimized for peak performance.

Stay connected and share your experiences with BMS connections. Together, we can continue to explore and refine this critical aspect of battery management, driving innovation and sustainability in the industry.

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