How to Select the Right Battery Cells for Custom Battery Packs?

Battery cells are the core components of a lithium battery pack. The selection of suitable cells directly affects battery performance, safety, size, weight, and operating life.

For companies developing electric vehicles, industrial equipment, robots, medical devices, marine systems, and energy storage products, choosing the right battery cells is an important step in custom battery pack development.

A suitable battery cell should match the application requirements, including voltage, capacity, discharge performance, operating environment, and safety standards.

This article explains the key factors to consider when selecting battery cells for custom lithium battery packs.

1. Understand the Application Requirements First

Before selecting battery cells, it is important to understand how the battery pack will be used.

Different applications require different battery characteristics.

For example:

Electric Mobility

Applications:

• E-bike

• Electric scooter

• Electric motorcycle

• E-cargo bike

Key requirements:

• Suitable energy density

• Compact size

• Stable discharge performance

• Waterproof design

Industrial Equipment

Applications:

• AGV

• AMR robots

• Forklifts

• Cleaning machines

Key requirements:

• Long operating time

• Frequent charging and discharging

• Stable current output

• Communication capability

Energy Storage Systems

Key requirements:

• Long cycle life

• Safety performance

• Stable operation

Understanding the application helps determine the most suitable cell chemistry and configuration.

2. Select the Appropriate Battery Chemistry

Lithium battery cells are available in different chemical systems. Each type has different characteristics.

Lithium-ion NMC Cells

NMC (Nickel Manganese Cobalt) cells are commonly used in applications requiring high energy density.

Characteristics:

• Higher energy density

• Compact size

• Suitable weight design

Common applications:

• Electric bicycles

• Electric motorcycles

• Portable devices

• Power tools

NMC cells are often selected when space and weight are important factors.

LiFePO4 Battery Cells

Lithium iron phosphate (LiFePO4) cells are widely used in applications requiring stable operation.

Characteristics:

• Good thermal stability

• Long cycle life

• Suitable for repeated charging and discharging

Common applications:

• AGV and AMR robots

• Industrial equipment

• Marine batteries

• Solar energy storage

LiFePO4 cells are often considered for applications requiring long service periods.

Lithium Polymer Cells

Lithium polymer cells provide flexible design options.

Characteristics:

• Flexible shape

• Lightweight structure

Common applications:

• Drones

• Portable electronic devices

The selection depends on product design requirements.

3. Consider Battery Cell Size and Format

Battery cells are available in different physical formats.

Common cylindrical cell types include:

18650 Battery Cells

Typical features:

• Diameter: 18mm

• Height: 65mm

Applications:

• E-bike batteries

• Portable devices

• Industrial battery packs

Advantages:

• Mature production technology

• Flexible battery pack configuration

21700 Battery Cells

Typical features:

• Larger size compared with 18650 cells

Applications:

• Electric mobility

• High-capacity battery packs

• Industrial equipment

Advantages:

• Higher capacity per cell

• Reduced number of cells needed for some designs

The choice between 18650 and 21700 depends on:

• Battery size requirements

• Capacity requirements

• Production design

4. Match Battery Cell Capacity Requirements

Cell capacity determines the total energy available in the battery pack.

For a battery pack:

Battery Energy (Wh) = Voltage (V) × Capacity (Ah)

When selecting cells, manufacturers need to consider:

• Required operating time

• Equipment power consumption

• Available installation space

For example:

A device requiring longer operation time may need:

• Higher capacity cells

• More parallel cell connections

• Larger battery pack design

The battery capacity should match the equipment requirements rather than simply selecting the largest capacity available.

5. Evaluate Discharge Current Performance

Different devices require different discharge capabilities.

Important parameters include:

• Continuous discharge current

• Maximum discharge current

• C-rate

Applications with high current demand include:

• Electric vehicles

• Power tools

• Drones

• Industrial robots

Applications with lower current requirements may focus more on:

• Capacity

• Cycle life

• Stability

The selected cell should provide enough current output for both normal operation and peak load conditions.

6. Consider Battery Cycle Life

Cycle life refers to how many charge and discharge cycles a battery can complete before capacity decreases.

Applications with frequent daily use usually require cells with suitable cycle performance.

Examples:

Industrial equipment:

• AGV

• Automated machinery

may require batteries that operate through many charging cycles.

Energy storage systems:

• Require long-term operation

Cycle life depends on:

• Cell chemistry

• Charging conditions

• Operating temperature

• Depth of discharge

7. Check Cell Consistency and Quality

Cell consistency is important when multiple cells are connected together.

Battery manufacturers usually evaluate:

• Voltage consistency

• Internal resistance consistency

• Capacity consistency

Good cell matching helps improve:

• Battery balance

• Charging efficiency

• Pack reliability

During production, battery manufacturers may perform cell sorting before assembly.

8. Consider Operating Temperature

Temperature affects battery performance and safety.

When selecting cells, consider:

• Charging temperature range

• Discharging temperature range

• Storage conditions

For applications in cold or hot environments, additional designs may be required:

• Temperature monitoring

• Heating systems

• Thermal management

Examples:

Outdoor equipment, marine applications, and industrial vehicles often require temperature considerations during battery design.

9. Check Safety Requirements and Certifications

Battery cells used in custom packs need to meet applicable safety requirements.

Common standards include:

• UN38.3

• IEC 62133-2

• CE

• UL standards

• RoHS

For international markets, certification requirements should be confirmed during the design stage.

Using suitable certified cells can support smoother product testing and market entry.

10. Work With an Experienced Battery Pack Manufacturer

Selecting battery cells is only one part of battery pack development.

A professional battery manufacturer can support:

• Cell selection

• Electrical design

• Battery configuration

• BMS integration

• Structural design

• Testing

• Certification preparation

The manufacturer can evaluate whether the selected cells match the complete battery system.

Common Questions About Battery Cell Selection

What factors should be considered when selecting lithium battery cells?

Key factors include battery chemistry, capacity, voltage, discharge current, cycle life, temperature range, size, and certification requirements.

Is 18650 or 21700 better for custom battery packs?

Neither type is suitable for all applications. The choice depends on battery capacity, size limitations, power requirements, and product design.

Are LiFePO4 cells suitable for industrial battery packs?

Yes. LiFePO4 cells are commonly used in industrial applications because of their stable characteristics and cycle performance.

How many cells are needed for a custom battery pack?

The number of cells depends on required voltage, capacity, and current output. Battery engineers calculate the series and parallel configuration based on application requirements.

Conclusion

Selecting the right battery cells is an important part of custom lithium battery pack development.

The selection process should consider battery chemistry, cell format, capacity, discharge performance, cycle requirements, operating environment, and safety standards.

A suitable battery cell configuration helps create a battery pack that matches the equipment requirements and provides stable operation.

By working with an experienced lithium battery manufacturer, companies can receive support in cell selection, battery design, testing, and production to develop battery solutions for different applications.