Custom Lithium Battery Pack Design: From Requirements to Production

Introduction

A custom lithium battery pack is more than a group of battery cells assembled together. It needs to match the electrical, mechanical, communication, and operating requirements of the device it powers.

From the initial requirements to cell selection, BMS design, mechanical structure, prototyping, testing, and mass production, every stage can affect the final performance and reliability of the battery pack.

In this article, we explain the key stages involved in developing a custom lithium battery pack from requirements to production.

1. Understanding Customer Requirements

Key information we typically collect from customers includes:

• Device type and application

• Required voltage and capacity

• Expected operating time

• Maximum continuous and peak current

• Available battery compartment dimensions

• Connector type and pin configuration

• Charging method and input requirements

• Communication protocol requirements (SMBus, I²C, CAN, RS485, etc.)

• Operating environment and temperature range

• Target production quantity

• Required certifications and compliance standards

Contact us to obtain the "Custom Battery Information Form"

2. Battery Chemistry & Cell Selection

Different applications require different battery technologies. Choosing the right chemistry is a critical decision that affects performance, safety, cost, and lifespan.

Lithium-Ion (Li-ion)

Li-ion batteries offer high energy density, relatively low weight, and flexible pack configurations. They are widely used in portable electronics, medical devices, industrial instruments, robotics, surveying equipment, and other professional devices.

Typical applications include:

• Portable consumer electronics
  
• Medical monitoring devices
  
• Industrial measurement instruments
  
• Robotics and automation
  
• Surveying and construction equipment 

Lithium Iron Phosphate (LiFePO4)

LiFePO4 batteries are known for excellent safety, long cycle life (3000+ cycles), and stable performance. They are particularly suitable for applications requiring frequent cycling, higher capacity, or long-term operation.

Typical applications include:

• Energy storage systems
  
• UPS backup power
  
• Portable power equipment
  
• Industrial equipment
  
• Outdoor power systems
  
• Backup power applications

Nickel-Metal Hydride (Ni-MH)

Ni-MH battery packs remain useful for many professional and industrial applications. They provide reliable performance, good durability, and wide operating temperature capability.

The right chemistry should be selected according to the device's power requirements, operating environment, expected cycle life, and safety requirements.

Cell Selection

Once the chemistry is determined, the next step is selecting the appropriate cell format. Cell options include cylindrical cells (18650, 21700, etc.), prismatic cells, and pouch cells. Factors such as cell capacity, discharge capability, cycle life, operating temperature, and application requirements all need to be considered when selecting battery cells.

3. Electrical Battery Pack Design

After determining the chemistry and cell type, the battery pack's electrical configuration needs to be designed to meet the device's voltage and current requirements.

Series and Parallel Configuration

• Series connection increases voltage. For example, connecting cells in series (3S, 4S, etc.) multiplies the nominal voltage by the number of cells in series.
  
• Parallel connection increases capacity and current capability. Connecting cells in parallel (1P, 2P, etc.) multiplies the capacity by the number of cells in parallel.

For example:

• A 3S1P configuration (3 cells in series, 1 in parallel) provides approximately 11.1V at the same capacity as a single cell.

• A 3S2P configuration (3 cells in series, 2 in parallel) provides approximately 11.1V with double the capacity of a single cell.

The battery configuration is designed according to the required voltage, capacity, current output, and available installation space.

4. BMS & Protection Design

A Battery Management System (BMS) plays an important role in protecting and monitoring lithium battery packs. It is an essential component for ensuring safety and reliability in custom battery designs.

A BMS can provide protection and monitoring functions such as:

• Overcharge protection – Prevents the battery from being charged beyond its safe voltage limit

• Over-discharge protection – Prevents the battery from being discharged below its safe voltage limit

• Over-current protection – Protects against excessive current draw that could damage cells

• Short-circuit protection – Disconnects the battery in case of a short circuit

• Temperature monitoring – Monitors cell temperature and shuts down if unsafe temperatures are detected

• Cell balancing – Equalizes voltage between cells to maintain pack capacity and prolong life

• Battery status monitoring – Tracks state of charge (SOC), state of health (SOH), and other parameters

For intelligent equipment, the battery may also need to communicate with the device.

Depending on the application, communication functions such as SMBus, I²C, CANBUS, RS485, and HDQ can be integrated.

The BMS should therefore be selected according to both the battery chemistry and the requirements of the host device.

5. Mechanical Structure & Connector Design

Battery space is often limited inside a device. A custom battery pack may need to match specific dimensional and mechanical requirements.

A custom battery pack may need to be designed around:

• Length, width, and height limitations

• Connector type and position

• Cable length and direction

• Mounting points and installation method

• Housing shape

• Internal component layout

• Accommodation for existing device structures

For products with limited internal space, the battery may need to be designed around the device's existing structure. This is especially important for medical devices, handheld instruments, robots, surveying equipment, portable electronics, and professional equipment.

The battery pack is designed to fit the device rather than forcing the device to accommodate a standard battery.

Even when the voltage and capacity are correct, an incompatible connector or pin configuration can prevent the battery from working properly. For OEM battery projects, the connector and wiring can be customized according to the device requirements.

6. Prototype Development

After the battery design is confirmed, a prototype can be produced for initial evaluation and testing.

The prototype development process typically follows this sequence:

1. Design – Finalize electrical and mechanical design based on customer requirements

2. Prototype – Build prototype samples using selected cells, BMS, and housing

3. Evaluation – Test the prototype for fit, electrical performance, and communication

4. Modification – Make necessary adjustments based on test results

Prototype samples allow customers to verify fit, electrical performance, and communication before mass production. This stage reduces risk and ensures that the final product meets expectations.

7. Testing & Validation

Testing is an essential step to ensure battery safety, reliability, and long-term stability.

Key tests typically include:

• Electrical performance testing – Verifies voltage, capacity, and current characteristics

• Charge and discharge testing – Confirms charging behavior and runtime performance

• BMS protection testing – Validates overcharge, over-discharge, over-current, and short-circuit protection functions

• Capacity testing – Confirms actual capacity meets specifications

• Aging testing – Evaluates long-term performance and cycle life

• Temperature testing – Verifies performance across the specified temperature range

• Reliability testing – Confirms performance under vibration, shock, and other operating conditions

8. Mass Production

Once the prototype is approved and testing is complete, the battery pack can move into mass production.

The mass production process typically includes:

1. Cell inspection – Incoming quality check of battery cells

2. Cell matching – Grouping cells with similar characteristics for consistent performance

3. Welding and assembly – Connecting cells using spot welding or other methods

4. BMS integration – Installing and connecting the BMS

5. Housing assembly – Encasing the battery in its housing

6. Testing – Final testing to verify performance and safety

7. Packaging – Packing finished batteries for shipment

Once the prototype is approved, the battery pack can move into mass production under controlled manufacturing and quality inspection procedures.

Looking for a Custom Lithium Battery Pack?

Whether you need a compact battery for a portable electronic device or a high-capacity solution for professional equipment, our engineering team can develop a battery pack based on your application requirements.

For 3C and consumer electronics projects, contact us to request our Custom Battery Project Development Information Form and provide your project requirements.