Does a Custom Lithium Battery Pack Need UN 38.3 Testing?

When developing a custom lithium battery pack for a specific device or application, OEMs often start by selecting cells that meet their required voltage, capacity, and performance specifications. The cell supplier may already provide UN 38.3 test documentation, which raises an important question: Can these existing test results cover the finished battery pack, or does the custom design need additional testing?

The answer depends on the battery type, its configuration, and the scope of the existing test documentation. Under the UN Manual of Tests and Criteria, lithium cells and lithium batteries are subject to different testing requirements. For rechargeable lithium battery types, applicable battery-level requirements also apply when the batteries are assembled from previously tested cells.

This distinction matters when an OEM changes the cell configuration, integrates a battery management system (BMS), or develops a new enclosure. Understanding these requirements early can help avoid documentation gaps and unexpected testing work later in the development process.

Does a Custom Lithium Battery Pack Need UN 38.3 Testing?

UN 38.3 refers to the testing requirements in Part III, subsection 38.3 of the UN Manual of Tests and Criteria. It establishes a series of design tests that lithium cells and batteries must pass before they can be offered for transport, subject to the applicable transport regulations.

Whether a custom battery pack needs testing depends on whether the finished design is already covered by a tested battery type and which requirements apply to that type. A cell's existing UN 38.3 test results do not automatically demonstrate that a separately developed battery pack has met the applicable battery-level requirements.

Cell-Level Testing vs. Battery Pack Testing

A lithium cell and a lithium battery are not interchangeable terms under UN 38.3. A battery generally consists of two or more cells electrically connected by permanent means, together with the components needed for its use, such as a case, terminals, and markings. A single-cell battery is treated separately under the Manual's definitions.

The testing scope also differs:

• Lithium cell types: All lithium cell types are subject to tests T.1 to T.6 and T.8.
• Non-rechargeable lithium battery types: These are subject to tests T.1 to T.5, including battery types composed of previously tested cells.
• Rechargeable lithium battery types: These are subject to tests T.1 to T.5 and T.7, including battery types composed of previously tested cells.

The Manual also provides a specific rule for component cells that are not transported separately from the battery they form part of: these cells need only undergo tests T.6 and T.8. This provision concerns the component cells and should not be confused with the testing requirements applicable to the completed battery.

When Is Additional Testing Required?

Additional testing may be necessary when a custom battery pack represents a different battery type from the one covered by existing test documentation.

For example, an OEM may use tested lithium-ion cells but develop a pack with a different series and parallel configuration, protection system, or mechanical structure. The engineering team must assess whether the resulting design is covered by an existing tested type or should be treated as a new type under UN 38.3.

Under subsection 38.3.2.2, certain changes to a tested rechargeable cell or battery can result in a new type. These include:

• A change of more than 20% in nominal energy, measured in watt-hours.
• An increase of more than 20% in nominal voltage.
• A change that might lead to failure of any of the prescribed tests.

The Manual identifies examples of potentially relevant design changes, including changes to electrode or electrolyte materials, protective devices, safety design, the number of component cells, and the way component cells are connected.

Not every modification automatically requires a complete new test programme. The impact of the change must be assessed against the tested design and the relevant requirements. OEMs should therefore verify the scope of existing documentation before relying on it for a modified battery design.

What Battery Design Factors Affect UN 38.3 Testing Requirements?

A custom battery pack combines electrical, electronic, and mechanical components. Each can affect the final design and its relationship to an existing tested battery type.

For this reason, UN 38.3 considerations should be included when defining the battery architecture, rather than being left until the pack is ready for shipment.

Cell Type and Battery Configuration

Cell selection is one of the first decisions in a custom battery project. Different cell chemistries, formats, dimensions, and electrical characteristics can affect the battery's design and testing considerations.

The configuration also matters. Changing the number of cells connected in series or parallel can affect nominal voltage, capacity, total energy, and the physical arrangement of the battery.

OEMs should define:

• Cell chemistry and format, such as cylindrical, prismatic, or pouch cells.
• Cell manufacturer and model.
• Series and parallel configuration.
• Nominal voltage and capacity.
• Total nominal energy in watt-hours.

These specifications provide the baseline for evaluating the proposed battery architecture and comparing it with existing cell or battery documentation.

Battery Capacity and Energy Rating

Battery capacity and nominal energy are important specifications for both system design and transport classification.

For a rechargeable battery, nominal energy is generally calculated using nominal voltage and rated capacity:

For example, a battery with a nominal voltage of 48 V and a rated capacity of 100 Ah has a nominal energy of 4,800 Wh.

The nominal energy rating should be consistent across the battery specification and UN 38.3 Test Summary. It also provides an important reference when assessing changes to a tested rechargeable battery type.

BMS and Protection Design

The battery management system is responsible for monitoring and controlling key battery operating conditions. Depending on the application, its functions may include cell voltage monitoring, temperature monitoring, current protection, balancing, and communication with the host equipment.

BMS hardware and software can also be relevant to UN 38.3 design-change assessments. The Manual identifies changes to protective devices, including hardware and software, as examples of modifications that might lead to failure of a prescribed test.

When defining a custom battery pack, OEMs should consider:

• Overvoltage and undervoltage protection.
• Overcurrent and short-circuit protection.
• Temperature monitoring and protection.
• Cell balancing strategy.
• Communication interfaces, such as CAN or RS485, where required by the application.

The protection strategy should be documented as part of the battery specification, including the hardware and software configuration used in the final design.

Battery Enclosure and Mechanical Structure

The enclosure protects the cells and internal components while providing the mechanical interface between the battery and the host equipment.

Its design may include mounting points, structural supports, insulation, connectors, and provisions for thermal management. These features can affect the battery's mass, dimensions, and mechanical behaviour.

For OEM projects, enclosure requirements should be defined alongside the electrical specifications. Important considerations include:

• Available installation space and mounting method.
• Enclosure material and structural design.
• Connector location and cable routing.
• Insulation and protection requirements.
• Cooling or heat dissipation arrangements.
• Operating environment, including vibration and temperature conditions.

An enclosure change does not automatically require new UN 38.3 testing, but modifications that might affect a prescribed test result should be assessed against the existing tested design.

What Should OEMs Prepare Before Starting a Custom Battery Project?

Clear project requirements help battery manufacturers evaluate the design, select suitable cells, and identify potential compliance considerations before prototype development.

OEMs do not need to finalise every technical detail at the beginning. However, preparing the following information can make the initial engineering assessment more accurate.

Electrical and Performance Requirements

Start with the electrical requirements of the equipment or system that the battery will power.

Relevant information includes:

• Required nominal voltage and operating voltage range.
• Target capacity and energy rating.
• Continuous and peak discharge current.
• Charging current and charging method.
• Expected operating time and duty cycle.
• Required cycle life and service life.
• Communication protocols and data requirements.

This information gives the engineering team a clear starting point for evaluating cell options and defining the battery's electrical performance.

For a practical example of the information needed when specifying a custom UPS battery, see custom lithium UPS battery requirements.

Mechanical and Environmental Requirements

The battery must fit the available installation space and operate under the conditions expected in the application.

OEMs should provide:

• Maximum battery dimensions and weight.
• Mounting position and mechanical interface.
• Connector type and terminal position.
• Operating and storage temperature ranges.
• Vibration, shock, and other environmental conditions.
• Cooling, ventilation, or thermal management requirements.

Where the battery will be installed in industrial equipment, medical devices, backup power systems, or other specialised applications, the OEM should also identify any application-specific safety and integration requirements.

Transportation and Compliance Requirements

Transportation requirements should be discussed before the final battery design is approved.

OEMs should clarify:

• Whether batteries will be shipped separately or installed in equipment.
• Expected transport modes, such as air, sea, or road.
• Destination markets and applicable transport regulations.
• Required UN 38.3 documentation.
• Any additional product, system, or market-specific compliance requirements.

UN 38.3 addresses the design testing of lithium cells and batteries for transport. It does not replace all other transport obligations. Packaging, marking, labelling, documentation, and shipment conditions must also be checked against the applicable rules, such as ADR for road transport, the IMDG Code for sea transport, and the IATA Dangerous Goods Regulations for air transport.

Defining these requirements early helps the OEM and battery manufacturer identify the documentation and testing work that may be needed before shipment.

How Can an ODM Battery Manufacturer Support UN 38.3 Compliance?

For OEMs developing a battery with specific electrical, mechanical, and communication requirements, an ODM partner can help connect product design decisions with testing and documentation considerations.

The manufacturer's role is to support the engineering process and coordinate the necessary compliance work. UN 38.3 testing itself must be conducted by a qualified testing facility, and the applicable test documentation should correspond to the actual cell or battery type.

ACE Battery provides custom battery design and manufacturing support for OEM/ODM projects, helping customers address battery requirements from cell selection and pack architecture to BMS integration and prototype development.

Cell Selection and Battery Pack Design

An ODM battery manufacturer can help evaluate cell options against the OEM's voltage, capacity, discharge, charging, size, and operating requirements.

The selected cells then form the basis of the battery pack architecture, including the series and parallel configuration, electrical connections, enclosure, and protection strategy.

At this stage, the manufacturer should also review available cell-level documentation and identify whether the proposed battery design may require its own applicable UN 38.3 testing.

BMS Integration and Prototype Development

The BMS must be designed around the battery configuration and the requirements of the host equipment. This includes defining protection functions, monitoring parameters, communication interfaces, and system integration requirements.

Prototype development allows the OEM and manufacturer to evaluate whether the battery meets its electrical, mechanical, and functional specifications.

Prototype evaluation also allows the engineering team to identify design issues, verify system integration, and prepare the technical information needed for subsequent testing.

For more information about battery communication and integration considerations, see custom battery pack design and integration.

Testing Coordination and Documentation

Once the battery design is sufficiently defined, the manufacturer can support the preparation of samples and technical information for the applicable UN 38.3 testing.

OEMs should pay attention to the relationship between the test documentation and the battery being purchased. Under subsection 38.3.5, the Test Summary includes information such as the manufacturer, testing laboratory, report reference, test date, battery description, model number, watt-hour rating, and test results.

When reviewing a supplier's documentation, confirm that:

• The manufacturer and battery model correspond to the product being supplied.
• The physical description, mass, and watt-hour rating are consistent with the battery specification.
• The listed tests and results are appropriate for the battery type.
• The document references the applicable edition of the UN Manual of Tests and Criteria.
• Any relevant assembled-battery testing information is included.

A Test Report contains the detailed records of the testing performed, while a Test Summary provides the standardised information required under subsection 38.3.5. OEMs should request the Test Summary for the actual cell or battery type and clarify the availability of the supporting Test Report where needed.

Plan UN 38.3 Requirements Early in Your Custom Battery Project

For OEMs developing custom lithium battery packs, UN 38.3 should be considered alongside cell selection, battery configuration, BMS design, and mechanical integration.

Reviewing the final battery configuration against existing test documentation before design approval helps OEMs identify potential testing gaps and plan the required compliance work.

Early coordination between the OEM and battery manufacturer helps establish the testing scope, documentation requirements, and project responsibilities before the battery enters production.