Power Battery Immersion Testing: Standards, Methods and Safety Requirements

Power battery immersion testing evaluates the sealing integrity, electrical safety, and abuse tolerance of lithium-ion cells, modules, and battery packs when fully submerged in fresh water or saline solution. As electric vehicles increasingly operate in flooded road conditions and coastal environments, this test has become a critical validation requirement under standards such as GB/T 31467.3, GB 38031, UL 2580, IEC 60529, and ISO 20653. This article explains the test principles, sample types, procedures, acceptance criteria, and typical industrial applications of immersion testing for traction batteries.

Technical Overview

Power battery immersion testing is a safety and environmental validation method in which a battery cell, module, pack, or enclosure is completely submerged in water—typically a sodium chloride solution simulating seawater—for a defined period. The test simultaneously stresses two aspects of battery design: the mechanical sealing capability of the enclosure (protection against water ingress) and the electrochemical and thermal stability of the battery when exposed to conductive liquid and potential internal short circuits.

In real-world service, traction batteries may encounter flooded roads, storm surge, vehicle wading, marine transport, and high-humidity coastal atmospheres. Water entering a high-voltage battery enclosure can cause insulation breakdown, external short circuits, electrolyte contamination, corrosion of busbars and connectors, and in severe cases thermal runaway. Immersion testing therefore verifies that the battery does not ignite, explode, leak hazardous material, or lose critical insulation performance when submerged.

The test is referenced in several national and international frameworks, including GB/T 31467.3 and GB/T 31485 (Chinese national standards for lithium-ion traction batteries), GB 38031 (safety requirements for electric vehicle traction batteries), UL 2580 (batteries for electric vehicles), IEC 60529 and ISO 20653 (IPX7 and IPX8 ingress protection classification), and IEC 62660-3 (safety requirements for secondary lithium cells). Accredited third-party laboratories typically perform the test for type approval, regulatory compliance, and R&D validation.

Testing Samples

Battery Cells

Cylindrical, prismatic, and pouch cells can be subjected to seawater immersion testing, typically in a saline solution with a sodium chloride concentration of approximately 3.5%. Cell-level testing evaluates the robustness of the cell can, seal, and terminal insulation against conductive liquid exposure.

Battery Modules

Modules are tested to assess how cell grouping, intercell busbars, and module-level covers behave under submersion. Module testing is often used during development to qualify sealing strategies before full pack-level validation.

Battery Packs and Systems

Complete battery packs, including enclosures, venting devices, high-voltage connectors, service disconnects, and the battery management system (BMS), represent the most common test objects. Pack-level immersion testing verifies the overall sealing design, insulation resistance, pressure equalization vent behavior, and post-immersion functional status of the thermal and electrical architecture.

Enclosures and Sealing Subassemblies

Battery housings, cable glands, cover gaskets, and vent valves may be tested independently to classify their ingress protection (IPX7 or IPX8) before integration, supporting design verification and supplier quality control.

Testing Items

Depending on the applicable standard and the engineering objective, the following test items are commonly performed:

• Seawater immersion test: full submersion in a 3.5% sodium chloride solution for a specified duration, commonly 2 hours, with observation for fire and explosion.
• IPX7 verification: immersion at approximately 1 meter of water depth for 30 minutes to confirm protection against temporary submersion.
• IPX8 verification: continuous immersion at a depth and duration agreed between manufacturer and purchaser, covering permanent or deep submersion conditions.
• Fresh water immersion: submersion in deionized or tap water for wading-condition simulation or comparative studies.
• Insulation resistance measurement: high-voltage insulation verification before and after immersion.
• Water ingress inspection: teardown, borescope examination, humidity indicator check, or mass comparison to detect internal leakage.
• Post-test functional check: BMS communication, contactor operation, voltage stability, and self-discharge monitoring after removal from the solution.

Testing Methods

A typical immersion test follows a structured sequence to ensure repeatability and traceability:

• Sample preparation: the battery is brought to the state of charge specified by the applicable standard or the customer test plan, surface temperature is stabilized at ambient conditions, and baseline data (voltage, insulation resistance, mass) are recorded.
• Solution preparation: a sodium chloride solution is prepared with a concentration of approximately 3.5% and controlled temperature, usually near room temperature. Fresh water tanks are used for IPX7 and IPX8 procedures.
• Immersion: the sample is fully submerged with the highest point of the enclosure below the liquid surface by the depth required by the standard. For the seawater safety test, the submersion time is typically 2 hours; for IPX7 it is 30 minutes at 1 meter depth.
• Observation: the sample is monitored during immersion and throughout a defined post-immersion observation period for fire, explosion, smoke, or visible leakage of electrolyte.
• Post-test evaluation: the battery is retrieved, drained, and externally dried, after which insulation resistance, electrical function, and internal water ingress are assessed. Teardown inspection may be performed to examine corrosion, moisture paths, and seal integrity.

Acceptance criteria generally require that the battery exhibits no fire and no explosion, maintains adequate insulation resistance between high-voltage circuits and the enclosure, shows no unacceptable water ingress into the protected volume, and—where applicable—retains specified electrical function. Safety precautions during the test include remote monitoring, a fire-suppression-ready test cell, insulated handling tools, and controlled disposal of contaminated solution in accordance with environmental regulations.

Applications

Immersion testing supports multiple stages of the battery and vehicle lifecycle:

• Regulatory type approval: demonstrating conformity with national safety standards for electric vehicle traction batteries prior to market entry.
• Design verification: validating gasket selection, seam sealing, connector design, and venting strategies during pack development.
• IP classification: providing evidence for IPX7 or IPX8 marking of battery enclosures under IEC 60529 and ISO 20653.
• Failure analysis: reproducing water-related field failures, such as packs exposed to flooding or wading, to determine root cause.
• Maritime and transport safety: assessing battery behavior in humid or submerged conditions during sea transport and handling scenarios.
• Stationary and off-highway systems: extending the methodology to energy storage enclosures, construction machinery, and two- or three-wheeled electric vehicles exposed to harsh environments.

FAQ

What is the main pass criterion for power battery immersion testing?

The primary criteria are no fire and no explosion during and after the test, supported by maintained insulation resistance, no unacceptable internal water ingress, and, where required, preserved electrical function.

Why is a 3.5% sodium chloride solution used instead of fresh water?

A 3.5% NaCl solution approximates seawater and is significantly more conductive and corrosive than fresh water. It accelerates the detection of sealing weaknesses and better represents the worst-case flooding environment a traction battery may encounter.

How does the seawater immersion safety test differ from an IPX7/IPX8 test?

The seawater immersion safety test focuses on battery abuse behavior—confirming that the battery does not ignite or explode when exposed to conductive liquid—whereas IPX7 and IPX8 tests classify the enclosure's ability to prevent water from reaching internal components under defined submersion depths and durations.

How is internal water ingress detected after the test?

Common methods include visual and borescope inspection through teardown, comparison of pre- and post-test mass, internal humidity sensors, condensation observation, and dielectric or insulation measurements that reveal moisture-related degradation.

What state of charge should be used for testing?

The state of charge is defined by the applicable standard or the agreed test plan; many specifications require testing at the normal operating state of charge or at a high charge level to ensure conservative results. The selected condition should always be documented in the test report.