Lithium-Ion Batteries Submerged in Water: Hazards and Testing

This article has been updated to reflect the introduction of the ISO 3941:2026 Class L fire classification; updated regulatory standards for IP67 and IP68 waterproof testing; and new data regarding the environmental impact of battery fire runoff water.

When lithium-ion batteries are submerged in water, immediate and severe chemical reactions occur that compromise battery integrity. Water ingress leads to the hydrolysis of electrolyte solvents, dissolution of critical lithium salts, and internal short circuits. These catastrophic failures can rapidly escalate into thermal runaway, a self-sustaining exothermic reaction that releases highly flammable gases, heavy metals, and toxic runoff into the surrounding environment.

Key Takeaways

• Submerging lithium-ion cells initiates the hydrolysis of organic electrolytes and degrades cathode materials.
• Saltwater submersion significantly accelerates short circuits and internal corrosion due to high electrical conductivity.
• Thermal runaway in wet batteries generates explosive hydrogen gas and cannot be extinguished by standard methods.
• Laboratory testing against standards like IEC 62133 and UN 38.3 is required to validate waterproof battery enclosures.
• The ISO 3941:2026 update formally introduced Class L to categorize the unique hazards of lithium-ion battery fires.

How does water ingress cause battery hydrolysis?

The interaction between liquid water and the internal components of a lithium-ion cell causes rapid, irreversible degradation. Lithium-ion battery packs utilize organic electrolytes that are highly sensitive to moisture. When a cell seal fails and water breaches the casing, the water molecules immediately react with the lithium salts (such as LiPF₆). This reaction induces the hydrolysis of electrolyte solvents, depleting the electrolyte and generating byproducts that impede normal lithium-ion transport.

Dissolution of lithium salts lowers the ionic conductivity of the battery and severely unbalances the cell stoichiometry. This excess lithium loss frequently leads to plating issues on the anode. Simultaneously, contact with water degrades the structural integrity of cathode materials, such as lithium cobalt oxide.

Side reactions with hydrolysis products further accelerate this degradation, destroying the capacity of the battery even if the water does not completely flood the core. The combination of these chemical failures creates extreme battery safety concerns for any industry relying on portable power.

Freshwater versus saltwater exposure risks

The exact composition of the water dictates the speed and severity of the battery failure. While freshwater exposure initiates hydrolysis and material breakdown, saltwater introduces an aggressive secondary threat. Salt dissolved in water acts as a highly efficient electrical conductor, and the conductive saltwater rapidly bridges the electrodes and triggers severe internal short circuits.

Furthermore, saltwater introduces chloride ions into the chemical mix. These ions immediately begin corroding battery terminals and internal interconnects manufactured from copper and aluminum. Extensive corrosion leads to the rapid electrical isolation of cell components.

The combined effect of salt-induced short circuits and accelerated corrosion makes saltwater submersion exponentially more dangerous than freshwater exposure, requiring immediate intervention and specialized environmental testing to analyze the resulting damage.

The mechanics of thermal runaway in submerged cells

Thermal runaway is an uncontrolled, cascading chemical reaction within a battery cell that causes a rapid discharge of energy. If enough water collects inside the battery enclosure to create a short circuit, intense localized heating occurs. Because water facilitates this electrical bridge, the heat generated quickly exceeds the temperature limits of the surrounding materials.

As the temperature rises, the organic electrolytes inside the lithium-ion cell decompose and release flammable gases, including hydrogen. The combination of intense heat, fuel from the electrolytes, and the rapid expansion of gases frequently causes the battery casing to rupture violently. While submerging a battery limits atmospheric oxygen, the internal chemical decomposition provides enough fuel and heat to sustain the reaction underwater.

Organizations like the National Fire Protection Association (NFPA) strictly advise treating any flooded electric vehicle or submerged battery pack as a severe, ongoing fire hazard, noting that thermal runaway can be delayed and occur days or weeks after the initial water exposure. Evaluating how a cell behaves during these catastrophic failures requires precise thermal runaway testing. Laboratories utilize techniques such as Accelerating Rate Calorimetry to measure the exact onset temperature and heat generation rate that triggers an explosion, providing manufacturers with critical data for designing stronger thermal management systems.

Environmental and toxicological impacts of battery runoff

A secondary danger of submerged lithium-ion batteries involves the severe environmental toxicity of the resulting runoff. When a battery casing ruptures underwater, or when large quantities of water are used to cool a thermal runaway event, harmful internal chemicals leach directly into the surrounding ecosystem. Runoff waters from lithium-ion battery failures are highly contaminated.

Extensive laboratory analysis of fire-fighting run-off waters shows high concentrations of dissolved heavy metals, including nickel, manganese, cobalt, lithium, and aluminum. Additionally, the decomposition of lithium salts often produces hydrofluoric acid when exposed to moisture. These toxic elements settle into aquatic ecosystems and contaminate local water tables. Managing and testing this contamination requires advanced chemical analysis, emphasizing the need for comprehensive performance testing protocols to ensure battery casings do not easily breach and release these hazards during environmental disasters.

Laboratory testing standards for water ingress and battery safety

To prevent water-induced failures, manufacturers must submit their energy storage systems to rigorous third-party laboratory evaluations. These standardized tests guarantee that batteries can withstand moisture, humidity, and full submersion without posing a threat to users.

International standards dictate strict methodologies for evaluating battery safety. For example, the International Electrotechnical Commission (IEC) publishes IEC 62133, a vital standard detailing the safety requirements for portable sealed secondary lithium cells. Testing against this standard involves subjecting the battery to various environmental stressors to confirm that the seals remain intact and that the internal fail-safes operate correctly.

The United Nations UN 38.3 standard governs the global transportation of lithium-ion batteries. UN 38.3 requires battery packs to pass rigorous evaluations, including altitude simulation, vibration, and thermal cycling, verifying that the units will not fail if exposed to condensation or pressure changes during transit.

IP67 and IP68 waterproof testing protocols

For devices expected to operate in wet environments, engineers rely on Ingress Protection ratings to quantify a product’s water resistance. Achieving an IP67 or IP68 rating requires specific laboratory electrical testing and physical immersion trials.

During an IP67 evaluation, a laboratory submerges the battery enclosure in one meter of water for exactly 30 minutes. Technicians then meticulously inspect the unit for any signs of water intrusion or voltage drops. An IP68 certification demands even more stringent testing, typically involving deeper submersion for longer durations, determined by the manufacturer but strictly monitored by the lab.

Advanced lithium battery testing systems utilize ultrasonic welding inspections, continuous voltage monitoring, and airtightness leak detection to pinpoint microscopic weaknesses in the battery seal before mass production begins.

Regulatory updates for lithium-ion battery fire classifications

The unique characteristics of lithium-ion battery fires, specifically those triggered by water-induced short circuits, have prompted updates to international fire safety classifications. Traditional fire suppression strategies often fail against lithium-ion blazes because the reaction is self-sustaining and the water used can sometimes exacerbate the spread of conductive materials.

In response, the International Organization for Standardization (ISO) introduced a major update with ISO 3941:2026, officially establishing “Class L” specifically for lithium-ion battery fires. This classification separates electrochemical fires from standard electrical fires (Class E). A Class L designation acknowledges the high energy release, sustained thermal runaway mechanisms, and the severe re-ignition risks associated with lithium-ion technology.

By standardizing this classification, laboratories, manufacturers, and emergency responders can develop and test specific suppression agents that address the chemical complexities of the battery rather than relying entirely on water cooling.

Testing standard	Governing body	Primary focus	Water and environmental parameters
IEC 62133	International Electrotechnical Commission	Portable secondary cell safety	Evaluates safety under environmental stress and verifies enclosure integrity.
UN 38.3	United Nations	Transport safety requirements	Includes thermal cycling and vibration testing to simulate transit moisture and stress.
ISO 12405	International Organization for Standardization	Traction battery packs for vehicles	Contains specific dewing test procedures and humidity exposure evaluations.
UL 1642	Underwriters Laboratories	General safety of lithium-ion cells	Covers short circuit, overcharge, and thermal abuse under varied conditions.
ISO 3941:2026	International Organization for Standardization	Fire classification standards	Defines Class L specifically for electrochemical fires, including thermal runaway events.

Mitigating risks and ensuring regulatory compliance

Submerging lithium-ion batteries in water triggers destructive chemical reactions and internal short circuits that frequently result in violent thermal runaway and toxic emissions. To prevent these catastrophic failures, manufacturers must engineer robust, waterproof enclosures for their products. Rigorously validating these designs against established IEC, ISO, and UN standards ensures that modern energy storage systems remain safe and resilient under severe environmental stress.

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