Cylindrical Battery Pack Assembly Line Solution for 18650 21700 26650 32650 and 32700 Cells

ACEY supplies a semi-automatic assembly solution for lithium battery packs made with 18650, 21700, 26650, 32650 and 32700 cylindrical cells. The solution covers cell capacity grading, insulation paper application, OCV/ACIR sorting, polarity inspection, spot welding, BMS testing, finished-pack testing, heat-shrink packaging, coding and aging.

The line combines automatic cell processing with manual pack assembly. Operators transfer cells and packs between standalone machines, load the welding fixture, and carry out BMS mounting and wiring. Paper application, OCV/ACIR sorting and CCD polarity inspection use dedicated equipment, while the welding station can use manual or programmed automatic machines.

This semi-automatic configuration suits small-to-medium batch production and projects handling different pack models. The equipment list is selected from the cell specification and pack drawing, including the series-parallel arrangement, connecting strips and electrical test requirements. Each machine is configured for the formats required by the project.

View our cylindrical battery pack assembly line for equipment details.

Solution Overview

Assembly Process

Cell Capacity Grading → Insulation Paper Application → OCV/ACIR Sorting → Cell Arrangement → Polarity Inspection → Spot Welding → BMS Testing and Installation → Finished-Pack Testing → Heat-Shrink Packaging → Coding → Pack Aging

Equipment and Process Stations

How the Semi-Automatic Cylindrical Battery Pack Assembly Line Works

Step 1 — Battery Cell Capacity Grading

Before assembly, the cells are charged and discharged to measure usable capacity and basic performance.

The purpose is to prevent cells with vastly different capacities—resulting from charge depletion or loss during prolonged storage or transport—from being grouped into the same battery pack. Weaker cells limit the usable performance of the entire series or parallel assembly.

A lithium ion cell grading machine runs programmed charge-discharge cycles across multiple channels and records the data for each cell.

ACEY provides battery charge discharge machine for charge-discharge testing, capacity grading and cycle performance evaluation of cylindrical lithium cells including 18650, 21700, 26650, 32700, 32140 and 33140. These multi-channel systems enable manufacturers to assess cell capacity, voltage, current and consistency prior to sorting and pack assembly, with various current ranges to meet different production requirements.

Product Name	Battery Capacity Grading Machine		Custom
Type	Linear / Energy-feedback type
Compatible battery cells	18650 / 21700 / 26650 / 32650 / 32700
Specification	5V 3A / 6A
Number of Channels	256	512
Product			View More

Step 2 — Battery Cell Insulation Paper Pasting

Insulation paper is applied around the positive terminal after capacity grading.

This additional insulation helps separate the positive terminal area from the metal cell casing(Anode) during assembly.

An automatic insulation paper sticking machine cuts and applies the paper with consistent positioning. ACEY machines can be equipped with changeable tooling for different cylindrical cells.

Product Name	Insulation Paper Pasting Machine	Custom
Mould	Replaceable
Compatible battery cells	18650 / 21700 / 26650 / 32650 / 32700
Product		View More

Step 3 — Battery Cell OCV and ACIR Sorting

Capacity grading alone is not enough for final cell matching.

Before assembly, it is also necessary to measure the open-circuit voltage and AC internal resistance of the battery cells to ensure the consistency of the battery pack.

The measured values are compared with preset ranges, and the cells are automatically separated into different groups.

ACEY cylindrical battery sorting machines are available with standard 5-, 6-, or 11-channel configurations, with customized options also available. They can be integrated with branded testers such as the HIOKI BT3561 or other compatible instruments to measure open-circuit voltage (OCV) and AC internal resistance.

Product Name	Battery Sorting Machine			Custom
Cylindrical Battery	18650 / 21700 / 26650 / 32650 / 32700 / More
Mould	Replaceable
Barcode Scanner	Optional
Tester Brand	HK3561/HIOKI3561
Number of Channels	5	6	11
Product				View More

Step 4 — Cell Arrangement and Polarity Inspection
Sorted cells are placed into the required series-parallel arrangement using cell holders or dedicated fixtures.

Before welding, the positive and negative orientation of every cell should be checked.

For small production runs, this may be done manually. On semi-automatic and automatic lines, a CCD polarity vistual inspection machine is more reliable because it checks the complete cell group against the preset pattern.

Product Name	CCD Tester		Custom
Compatible Battery Cells	18650 / 21700 / 26650 / 32650 / 32700 / More
Camera	HD Industrial Camera
Loading Method	Manual Placement	Conveyor Belt Auto Feeding
Product			View More

Step 5 — Battery Pack Spot Welding
Spot welding is one of the most important operations in cylindrical battery pack assembly.

The cells are connected in series and parallel by welding nickel or nickel-plated connecting strips to the cell terminals.

The welding result is affected by more than welding current. The main process variables include:

• Strip material
• Strip thickness
• Cell terminal material
• Welding current
• Welding time
• Electrode pressure
• Electrode condition
• Welding point position

Product Name	Battery Pack Spot Welding Machine					Custom
Compatible Battery Cells	18650 / 21700 / 26650 / 32650 / 32700
Welding Power Supply	5000A / 8000A / 10000A
	DC Inverter / Transistor
Operation Mode	Manual		Automatic
Product						View More

Step 6 — BMS Testing and Installation

After the cell groups are electrically connected, the battery management system is installed according to the pack design.

Before installation, the BMS needs to be tested to verify its protection functions.

The BMS tester mainly check functions such as:

• Overcharge protection
• Overcharge recovery
• Overdischarge protection
• Overdischarge recovery
• Overcurrent protection
• Standby current
• Protection delay and recovery behavior

Product Name	BMS Test Equipment			Custom
Number of Series	4S / 16S / 20S / 24S / 32S / 52S / More
Over-Discharge Current	120A / 150A / 200A / 300A / 400A / 500A / 600A / 800A / More
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Step 7 — Battery Pack Comprehensive Testing
Once the BMS, wiring and electrical connections are complete, the battery pack is tested as a finished assembly.

This step checks components and connections introduced during battery pack assembly rather than the performance of an individual cell.

The battery comprehensive testing machine can be configured to test:

• Open-circuit voltage
• AC/DC internal resistance
• Rapid Charging
• Rapid Discharging
• Charge protection
• Discharge protection
• Overcurrent protection
• Short-circuit protection

Product Name	Battery Comprehensive Tester			Custom
Voltage	50V/60V/100V/120V/150V/More
Discharge Current	60A/120A/150A/200A/300A/400A/500A/600A/More
Product				View More

Step 8 — Battery Pack Heat Shrink Packaging

Upon completion of electrical testing, the battery pack proceeds to final packaging. For heat-shrink packaging processes, the battery pack is conveyed through a temperature-controlled shrink tunnel.

Available packaging options include:

• PVC
• POF
• PP (Polypropylene)
• PE (Polyethylene)
• Customized enclosure

Product Name	Heat Shrink Tunnel Machine			Custom
Model	ACEY-HSM4020C	ACEY-HSM4525C	ACEY-HSM5035C
Shrink Film	POF/PVC/PP	POF/PVC/PP/PE
Tunnel size(mm)	1200*400*200	1200*450*250	1200*500*350
Shrinkable Product Size(mm)	350*150	400*200	450*300
Product				View More

Step 9 — Battery Pack Coding and Traceability
Before aging test and shipment, unique identification marks are applied to each battery pack to realize full lifecycle traceability.

Printed information includes:

• Battery model
• Rated voltage
• Capacity
• Production date
• Batch number
• Serial number
• Barcode
• QR code
• More

ACEY provides handheld printers for small-batch production, plus conveyor-mounted and continuous inkjet printers for efficient production lines.

Product Type	Handheld Inkjet Batch Coding Machine	Automatic Inkjet Batch Coding Machine
Product			View More

Step 10 — Battery Pack Charge/Discharge Aging
Completed battery packs undergo programmable charge-discharge aging before shipment. The system records voltage, current, capacity and test time to assess pack performance and operating stability

ACEY provides battery pack charge discharge test equipment for a wide range of battery pack applications.

Product Name	Battery Aging Machine				Custom
Type	Linear / Energy-Feedback
Voltage	30V / 60V / 70V / 85V / 100V / 120V / 150V / 200V / More
Charge & Discharge Current	10A / 20A / 30A / 40A / 50A / 60A / 100A / 120A / More
Number of Channels	2 / 3 / 4 / 6 / 8 / 9 / 12 /14 / 16 / 18 / 24 / 36 / More
Product					View More

How to Configure Cylindrical Battery Pack Assembly Equipment

The equipment should be selected from the actual battery pack design rather than only from the cell model.

Two 21700 battery packs may require different fixtures, welding machines and test systems when their series-parallel configurations, current requirements and mechanical structures differ. The same applies when changing between 18650, 21700, 26650, 32650 and 32700 cells.

To configure the line, please provide the following information：

Cell Information

• Cell model
• Cell chemistry
• Cell capacity
• Nominal voltage
• Maximum charge/discharge current

Battery Pack Design

• Series and parallel configuration
• Number of cells
• Pack voltage
• Pack capacity
• Maximum working current
• Pack dimensions or drawing

Welding Information

• Nickel or nickel-plated strip material
• Strip thickness
• Busbar structure
• Welding pattern
• Number of welding points

BMS Information

• Number of series
• Protection current
• Communication function
• BMS drawing or datasheet

Production Requirement

• Packs per day, per month or per year
• Number of battery pack models
• Planned automation level
• Workshop layout
• Available operators

Testing Requirement

• Cell grading criteria
• OCV and ACIR sorting limits
• Finished pack test items
• Charge/discharge current
• Aging procedure
• Required test channels
• Data traceability requirements

These details are used to select the equipment, fixtures and test ranges required for the actual battery pack.

Frequently Asked Questions

*Can This Solution Support 18650, 21700, 26650, 32650 and 32700 Cells?
Yes. This solution can be configured for battery packs made with 18650, 21700, 26650, 32650 and 32700 cylindrical cells. Machines, molds and fixtures are selected to match the required cell dimensions and pack design.

*How Is the Spot Welding Machine Selected？
Selection depends on the pack dimensions, cell terminal, connecting strip material and thickness, and welding pattern. Manual, single-sided automatic and double-sided automatic options are available.

Request a Line Configuration and Quotation

Send ACEY the following information to discuss the equipment for your pack assembly project:

• Cell format, chemistry and capacity.
• Pack series-parallel configuration, nominal voltage, maximum charging voltage, capacity and working current.
• Pack dimensions or drawings.
• Connecting strip material, thickness and welding pattern.
• BMS specification, finished-pack test items and aging procedure.
• Required packs per hour or day and preferred automation level.

Contact ACEY for a cylindrical battery pack assembly line proposal and quotation.

For larger-format cells, explore our Semi-Automatic Battery Pack Assembly Line Solutions for 32140 & 33140.