As demand for lithium batteries continues to grow across e-bikes, AGVs, forklifts, energy storage systems, robots, and industrial equipment, manufacturing a lithium battery pack has become far more than simply connecting battery cells. It is a comprehensive process involving precision manufacturing, automated assembly, intelligent quality control, and full traceability.

For OEM customers, the quality of a battery pack depends not only on the cells used but also on the consistency of the manufacturing process, production technology, and inspection standards.

This article walks you through the complete manufacturing process of a high-quality lithium battery pack, from individual battery cells to a fully tested finished product.

Stage 1: Cell Sorting

Why Is Cell Sorting Important?

Even cells from the same production batch have slight differences in voltage, internal resistance, and capacity. Assembling unmatched cells can lead to:

• Capacity imbalance
• Higher internal resistance variation
• Increased voltage deviation
• Shorter cycle life
• Frequent BMS balancing
• Premature battery pack failure

To ensure consistency, premium battery manufacturers perform automated cell sorting before assembly.

Cell Sorting Parameters

Each battery cell is automatically tested for:

• Voltage
• Internal Resistance
• Capacity

Typical sorting standards include:

• Voltage deviation ≤ 5 mV
• Internal resistance deviation ≤ 0.5 mΩ
• Capacity deviation ±1%

Only qualified cells proceed to the next production stage.

Benefits:

• Improved cell consistency
• Longer cycle life
• Reduced heat generation
• Higher battery reliability

Stage 2: Laser Welding

After sorting, qualified cells are connected together.

Most premium battery packs use laser welding instead of traditional spot welding because it offers:

• Stronger weld joints
• Smaller heat-affected zones
• Higher automation
• Better welding consistency

Typical welding parameters include:

• Welding pressure: 0.2–0.4 MPa
• Welding current: Approximately 3000 A
• Weld nugget diameter: 2–3 mm

Laser welding significantly reduces the risk of weak or missing welds while improving overall pack reliability.

Stage 3: Module Stacking and Module Welding

Individual cell groups are assembled into battery modules.

This process includes:

• Module positioning
• Compression
• Module connection
• Busbar welding

Key quality controls include:

• Module flatness
• Module spacing
• Compression force
• Welding accuracy

A robust module structure improves vibration resistance and long-term durability.

Stage 4: CCS (Current Collection System) Assembly

The Current Collection System (CCS) monitors voltage and temperature throughout the battery pack.

The CCS typically includes:

• Voltage sensing wires
• NTC temperature sensors
• Signal connectors
• Flexible circuit boards

For example:

• 12 voltage sampling points
• 4 NTC temperature sensors

These signals are transmitted to the Battery Management System (BMS) for:

• Cell balancing
• Temperature monitoring
• Over-voltage protection
• Under-voltage protection

Accurate CCS installation is critical for precise BMS performance.

Stage 5: Laser Welding of Battery Terminals

The positive and negative terminals are then welded using high-power laser equipment.

Typical parameters include:

• Laser power: 1500–3000 W
• Welding speed: 80–150 mm/s
• Weld penetration: 0.5–1.2 mm

High-quality terminal welding minimizes electrical resistance and improves high-current discharge capability.

Stage 6: Battery Module Completion

After all electrical connections are completed, the battery module is assembled.

The process includes:

• Housing installation
• Module fixation
• Connector installation
• Structural fastening

This stage determines the mechanical strength and structural integrity of the battery module.

Stage 7: Battery Pack Assembly

Multiple battery modules are installed inside the battery enclosure.

To minimize mechanical stress, modules are generally installed from the center outward.

Typical assembly specifications include:

• Module spacing: Approximately 10 mm
• Fastening torque: Approximately 15 N·m

Proper assembly ensures the battery pack remains secure during transportation and operation.

Stage 8: High-Voltage Busbar Installation

High-voltage busbars connect the battery modules electrically.

Critical assembly requirements include:

• Copper busbar installation
• Contact surface treatment
• Conductive coating
• Torque-controlled fastening

Typical specifications include:

• Tightening torque: 20–25 N·m
• Contact resistance: <0.1 mΩ

Low contact resistance reduces heat generation, improves efficiency, and extends battery life.

Stage 9: BMS Installation and Wiring

The Battery Management System (BMS) serves as the brain of the battery pack.

This stage includes:

• BMS installation
• Voltage sensing harness connection
• Communication cable installation
• CAN/RS485 interface integration
• Waterproof connector installation

Proper cable routing helps:

• Reduce electromagnetic interference (EMI)
• Simplify maintenance
• Improve long-term reliability

Stage 10: Cooling System Installation (For Liquid-Cooled Battery Packs)

Large battery packs used in energy storage systems and electric vehicles often require liquid cooling.

The cooling system typically consists of:

• Cooling plates
• Water pump
• Coolant piping
• Expansion tank

After installation, the cooling circuit undergoes leak testing.

Typical test conditions include:

• Test pressure: 200 kPa
• Leakage rate: <0.1 mL/min

This ensures reliable thermal management throughout the battery’s service life.

Stage 11: Internal Harness Routing

Inside the battery pack, engineers organize:

• High-voltage cables
• Low-voltage cables
• Communication harnesses
• Voltage sensing wires
• Cooling pipelines

All wiring is carefully secured, insulated, and protected against vibration and abrasion.

A well-organized internal layout enhances safety, reliability, and serviceability.

Stage 12: Battery Pack Sealing

The battery enclosure is sealed by installing:

• Upper cover
• Rubber gasket
• Waterproof sealant
• Fastening bolts

Automated screw tightening and precision sealant dispensing ensure uniform sealing performance.

Stage 13: Helium Leak Testing

Once sealed, the battery pack undergoes a helium leak test.

The purpose is to verify:

• Airtightness
• Waterproof capability
• IP protection performance

Typical testing conditions include:

• Pressure holding time: 60 seconds
• Leakage rate: ≤50 Pa/min

Helium leak testing is widely used for EV and energy storage battery packs to ensure long-term sealing reliability.

Stage 14: Waterproof Testing (IP67/IP68)

The completed battery pack then undergoes waterproof validation.

Common tests include:

• Rain simulation
• Water immersion testing

Typical IP67 testing conditions:

• Water depth: 1 meter
• Immersion time: 30 minutes

Inspection items include:

• Water ingress
• Insulation resistance
• Bubble detection

Only battery packs meeting IP67 or IP68 standards proceed to the next stage.

Stage 15: End-of-Line (EOL) Testing

End-of-Line (EOL) testing is one of the most critical quality control procedures.

Comprehensive tests include:

• Insulation resistance
• Withstand voltage
• Airtightness
• Capacity verification
• Internal resistance
• State of Charge (SOC) calibration
• Communication testing
• BMS functional verification

Fully automated EOL systems ensure every battery pack meets design specifications before shipment.

Stage 16: Capacity and Performance Testing

Battery packs are tested inside a constant-temperature chamber under standardized charging and discharging conditions.

Typical testing conditions:

• Ambient temperature: 25 ± 2°C
• Standard charge/discharge rate

Performance verification includes:

• Actual capacity
• Energy output
• Discharge curve
• Performance consistency

Most manufacturers require the measured capacity to reach at least 95% of the rated capacity before approval.

Stage 17: Laser Marking and Final Quality Inspection

The final production stage includes:

• Laser marking
• Serial number generation
• QR code labeling
• MES system registration

This enables complete product traceability, including:

• Raw material tracking
• Manufacturing records
• Test data
• After-sales service history

After a final appearance inspection, the battery pack is ready for packaging and shipment.

Why Is a Standardized Manufacturing Process So Important?

A high-quality lithium battery pack is not defined solely by premium battery cells. It is the result of precision engineering, automated manufacturing, and rigorous quality control throughout every production stage.

From cell sorting and laser welding to BMS integration, waterproof sealing, End-of-Line testing, and full traceability, each manufacturing step directly impacts the battery pack’s safety, reliability, performance, and service life.

For OEMs, selecting a battery manufacturer with standardized production processes, advanced automation, and comprehensive quality inspection systems helps reduce failure rates, improve product performance, lower warranty costs, and strengthen market competitiveness.

Contact Us

Looking for a reliable custom lithium battery pack manufacturer?

Dongguan Yizhan Electronics Technology Co., Ltd. specializes in OEM & ODM lithium battery solutions for e-bikes, robots, AGVs, forklifts, energy storage systems, industrial equipment, and other electric applications.

We provide:

• Custom battery pack design
• BMS development
• Structural customization
• International certification support
• Automated manufacturing
• 100% End-of-Line testing
• Global OEM production services

Contact us today to discuss your custom lithium battery project and discover how our engineering team can power your next innovation.