Custom Battery Pack Design Process: From Idea to Production

The first step in a successful custom battery pack is to pick cells and connect them together. The design should take into account voltage, capacity, discharge current, space, charging type, working temperature, communication, protection, certification and uniformity of production.

The custom battery pack design process at GLOFLUX is a well-defined engineering process. The review of the device requirements, prototype validation and mass production all contribute to the reduction of technical risks and an improvement in battery compatibility.

Step 1: Collect the Product Requirements

The first step is to know how the battery will be used. It is important for the customer to give as much technical information as possible such as:

Nominal voltage
Required capacity or runtime
Continuous working current
Maximum or peak current
Battery compartment dimensions
Charging voltage and current
Operating temperature
Connector type and wire length
Communication requirements
Expected cycle life
Target certification
Estimated order quantity

When the whole specifications cannot be provided, customer can send drawings of the devices, a sample battery, a product prototype or electrical parameters of the product. Battery engineers can then consider the needs and suggest a sensible initial solution.

Step 2: Select the Battery Chemistry

Different battery chemistries provide different combinations of energy density, cycle life, discharge capability, dimensions and temperature performance.

Lithium-Ion Batteries

Cylindrical cells (e.g. 18650 or 21700) are typically chosen for industrial equipment, robots, portable electronics, lighting systems and other applications that demand consistent output and flexible capacities.

Lithium Polymer Batteries

The li pol pouch cell is light in weight and can be available in a variety of sizes. They are designed for smart wearable applications, medical devices, Bluetooth speakers, beauty products and small electronics with minimal internal space.

LiFePO4 Batteries

LiFePO4 batteries are frequently chosen for their cycle life, thermal stability, and long-term reliability, making them suitable for applications where these features are crucial. Common use is in robots, solar energy storage and lighting, and industrial equipment.

The final chemistry should be selected according to the actual application rather than capacity alone.

Step 3: Determine the Series and Parallel Configuration

Once the cell is chosen, the engineer works out the series and parallel combinations to get the desired voltage and capacity.

Series connection increases the battery voltage, and parallel connection increases the capacity and available current. The 3S configuration can, for instance, be used for a design to achieve a voltage grade, and more in parallel to increase runtime.

At this stage, engineers also consider:

Maximum charging voltage
Discharge cut-off voltage
Continuous discharge current
Peak load duration
Cell temperature rise
Available installation space
Pack weight
Required safety margin

The configuration must provide for normal operation as well as temporary high power operations when starting up, communicating wirelessly, moving the motor, etc.

Step 4: Design the BMS and Protection Circuit

The battery management system protects the cells and controls important electrical functions. A standard BMS may provide:

Overcharge protection
Over-discharge protection
Overcurrent protection
Short-circuit protection
Temperature protection
Cell balancing

Fuel gauge and data storing/communication with the host device are also required for more advanced battery packs. The communication can be UART, SMBus, I²C, CAN or RS485.

The protection limits should be the same as the ones selected and the device's operating properties. The protection level, if set too low, may cause the battery to turn off during peak demand. The cells might not get the protection desired if the setting is wrong.

Step 5: Complete the Mechanical Design

Arrangement of cells, BMS, wires, connector and insulation materials in the pack is dependent on mechanical structure.

Mechanical customization may include:

Cell arrangement
Heat-shrink packaging
Plastic enclosure
Metal housing
Battery holder
Connector position
Wire length and gauge
Charging and discharge ports
Mounting points
Labels and branding

Additionally, when designing a battery, engineers need to take vibration, impact, heat dissipation, assembly tolerance, and battery installation/replacement methods into account.

A 3D model of battery compartment may be useful for compact devices to help avoid potential interference with internal components. The replaceable battery enclosure, locking device and electrical contacts should facilitate the repeated installation and removal of replaceable batteries.

Step 6: Review Safety and Compliance Requirements

Design planning for certification should be started prior to the final design being "frozen. The applicable requirements depend on the battery chemistry, configuration, product category, transportation method and destination market.

Documentation and/or testing for UN38.3, IEC 62133, UL, CE, RoHS, MSDS or other product specific requirements may be involved in a project..

Customers are advised to specify the applications of their target markets early as changing the cell, BMS and mechanical structure after testing will need further evaluation. The manufacturer and the product certification team should thus coordinate before tooling and mass production start.

Step 7: Produce and Test Prototypes

Once the specification and drawings are approved, prototype battery packs are produced. The samples allow customers to verify whether the battery fits the device and performs correctly under realistic operating conditions.

Prototype evaluation commonly includes:

Physical fit and installation
Charging compatibility
Device startup
Runtime
Continuous and peak discharge
Connector polarity
Communication
Temperature rise
Protection functions
Mechanical stability

It is recommended that the customer perform a test on the battery inside the product if at all possible. A battery which works perfectly on a test bench can fail under actual load, when using motors, heating elements, wireless modules and other loads which fluctuate.

Step 8: Optimize the Design

Prototype testing can provide opportunities to enhance the battery. The capacity and cell configuration can be adjusted as well as BMS settings, the design of the cables, the design of the connector, the design of the housing or the insulation structure can be adjusted by the engineers.

Changes in the design should be recorded and verified prior to pilot production. By keeping the specification in control, purchasing, engineering and production and quality teams can all work from an approved copy of the specification.

Step 9: Conduct Pilot Production

Pilot production verifies whether the battery can be manufactured consistently using the intended materials, equipment and assembly procedures.

During this stage, the manufacturer reviews:

Cell matching
Welding consistency
BMS assembly
Insulation placement
Wiring and connector assembly
Housing fit
Test procedures
Production records
Packaging methods

Any assembly issue discovered during pilot production should be corrected before a larger order is released.

Step 10: Begin Mass Production and Quality Control

Once they have passed their pilot batch, the battery enters mass production. Incoming material inspection, in process checks, electrical test, aging and final appearance inspection are all examples of quality control.

In custom projects, it is especially crucial to have traceability. The production record should contain the approved cell, BMS version, connector, wire specification, housing and other critical materials.

GLOFLUX provides customers with support from the very beginning of the battery need to cell selection, to BMS integration and to the design and creation of the enclosure and prototype to production. A structured process to develop an application concept into a battery solution for repeatable manufacturing.

Conclusion

The design process for the custom battery pack bring together the electrical engineering, mechanical structure, safety protection, compliance planning, and manufacturing control aspects. Any of these steps can result in inadequate run time, unscheduled shutdowns, excessive temperature increases, installation issues or production delays.

If an OEM customer engages a knowledgeable battery manufacturer early, they are able to pinpoint technical risks before finalizing the design of the device and develop a battery pack that is optimized according to the needs of the device, market and manufacturing.

Frequently Asked Questions

1. To design a custom battery pack what information is required?

The primary parameters are voltage, capacity, working current, peak current, size and shape, connector, charging method, temperature range and estimated order quantity.

2. How long does custom battery development take?

The timeline is dependent on cell availability, BMS complexity, enclosure tooling, quantity of prototype, testing and certification plans.

3. Can an existing battery pack be redesigned?

Yes. Customers can submit the original battery and/or device details and/or specifications for compatibility testing and possible performance enhancements.

4. Can GLOFLUX customize the BMS and communication protocol?

It is possible to assess BMS protection parameters and communication functions based on the application – UART, SMBus, CAN, RS485 etc.

5. Should certification be considered before prototyping?

Yes. Target markets and certification requirements should be identified at an early stage as cell selection and pack configuration and structural changes can impact on testing.