The process of assembling lithium battery cells into complete battery pack is called battery PACK. It involves integrating key components such as battery cells, protection board, nickel strips and labeling materials. Through series of processing and assembly steps, these parts are combined into fully functional battery pack. Apsen Battery will share how to design and assemble lithium battery packs properly—let’s dive in and learn together.

What is a Lithium Battery Pack?

Lithium battery pack is a circuit system made up of multiple lithium battery cells that work together to provide power. These packs act as rechargeable energy sources capable of storing charge and delivering energy to devices.

Each pack can consist of multiple cells, and each cell comes with its own voltage and capacity. By connecting the cells in series or parallel, the battery pack can deliver higher voltage or greater energy output, depending on the configuration. Charging system is typically connected to the battery pack to supply power to the target devices.

The size of a battery pack depends on the type and number of battery cells it contains. Commonly used cell formats include 18650, 21700, 26650, 32700, and prismatic (square) cells. The number of cells used directly influences the overall dimensions of the pack.

Step 1: Cell Sorting and Grouping

First step in assembling lithium battery pack is to sort and match the cells. Technicians group cells with similar performance characteristics to ensure consistency. During this sorting process, they carefully evaluate each cell based on key parameters such as internal resistance, voltage, rated capacity, charge/discharge efficiency, and self-discharge rate. By grouping cells with closely matched specifications, they improve internal consistency within the battery pack, which boosts overall efficiency and extends the service life of the module.

Step 2: Cell Assembly and Fixture Alignment

Next, the selected cells are assembled into a structured formation using fixtures, followed by spot welding to connect them. It’s essential to follow the Standard Operating Procedure (SOP) strictly during this step, especially to ensure that the cell polarity (positive and negative terminals) is aligned correctly. Proper alignment prevents short circuits and ensures electrical safety throughout the assembly.

Step 3: Welding the Battery Pack to the PCM/BMS

The third step involves welding the battery pack to the PCM (Protection Circuit Module) or BMS (Battery Management System). This component acts as the “heart” of the battery pack, protecting it from critical risks such as overcharging, over-discharging, and short circuits. These safety functions are crucial to prevent potential hazards like explosion, fire, or damage.

For low-voltage battery packs with fewer than 20 cells, a PCM with cell-balancing capabilities is ideal. This helps maintain voltage balance across all cells and extends battery life. For high-voltage packs with more than 20 cells, an advanced BMS is recommended. The BMS continuously monitors the performance of each cell in real time, ensuring safe and efficient operation of the entire battery system.

Step 4: Insulation of the Semi-Finished Battery Pack

At this stage, technicians apply insulation and secure the voltage sensing wires, output cables, and positive/negative terminals. During the installation, it’s crucial to avoid compressing or stacking the wires, especially the voltage sampling wires and main output leads. Excessive pressure can damage the insulation, increasing the risk of short circuits. Proper insulation ensures safety and reliability before moving on to final assembly.

Step 5: Testing the Semi-Finished Battery Pack

Once the battery cells are assembled and the BMS is connected, the pack undergoes a full range of tests to verify quality and performance. These tests include charge/discharge cycles, total internal resistance checks, overall capacity measurements, and safety tests such as overcharge, over-discharge, short-circuit, and overcurrent protection.

Depending on the application, additional rigorous testing may be required—such as high and low-temperature endurance, nail penetration, drop resistance, and salt spray corrosion. During these procedures, technicians closely monitor the battery’s response. For example:overcharge test, they check whether the BMS can handle high voltage safely；short-circuit test, they assess whether the system can withstand sudden surges in voltage and current；overcurrent test, they evaluate how well the BMS manages strong pulse currents.Only after all tests are successfully passed can the battery pack move on to the final packaging phase.

Step 6: Battery Pack Packaging

Based on the type of battery pack, the appropriate packaging method is selected. For packs using PVC wrapping, technicians place the pack into heat-shrinking machine for sealing. For packs housed in metal enclosures, they proceed with external casing assembly. Throughout the process, it’s important to handle the battery pack with care to avoid impact or compression. Proper insulation of wires must be maintained to prevent short circuits and ensure overall safety.

Step 7: Final Pack Testing

In the final testing phase, the completed battery pack is placed into a comprehensive battery tester with all required parameters configured. This test evaluates the battery pack’s total voltage, internal resistance, and basic charge/discharge performance. If needed, additional tests—such as overcurrent and short-circuit protection—can also be carried out to ensure full functionality and safety.

After completing all these steps, the lithium battery pack is fully assembled and tested. Designing and building a battery pack isn’t as complex as it may seem—just follow each step carefully, and you’ll be able to create a battery pack tailored to your specific needs.