Dual Considerations of Cost and Safety: Why Overweight Lithium Batteries Are Rejected by Global Air Cargo

In 2023, a cargo flight bound for Europe from Shenzhen Airport was urgently grounded before loading—security personnel discovered that a batch of lithium batteries declared as “24kg per unit” actually weighed 38kg, a serious overweight violation. Eventually, this shipment worth 5 million yuan was rejected by the airline. The shipper not only bore 200,000 yuan in liquidated damages but also suffered over 1 million yuan in losses due to delayed delivery caused by re-routing via land transport. This is not an isolated case: according to statistics from the International Air Transport Association (IATA), global air cargo rejected 12,000 batches of overweight lithium battery shipments in 2023, involving over 3 billion US dollars. On the surface, the rejection is strict enforcement of the “25kg critical limit”; fundamentally, it is an inevitable choice for the aviation industry under the dual pressures of “uncontrollable safety risks” and “soaring operational costs”. Overweight lithium batteries not only amplify thermal runaway risks but also drive up compliance, emergency response, and management costs across the entire logistics chain, making them a “high-risk, high-cost” 禁区 for global air cargo.

I. The Inviolable Safety Red Line: The Logic of Uncontrollable Risks for Overweight Lithium Batteries

The aviation industry’s rejection of overweight lithium batteries is primarily driven by the “exponential rise” in safety risks. When lithium battery weight exceeds the 25kg critical limit, the probability of thermal runaway, severity of harm, and difficulty of control increase non-linearly, exceeding the safety capacity of air transport systems and creating an “uncontrollable” risk exposure.

(1) Sharp Increase in Thermal Runaway Probability: From “Occasional Hazard” to “Inevitable Risk”

The thermal runaway risk of overweight lithium batteries first stems from the contradiction between “excessive packaging density” and “insufficient protection”. To fit more batteries into a single package and bypass weight limits, enterprises often reduce the thickness of cushioning materials and cut back on independent protective units, making batteries vulnerable to vibration and impact. Experiments by the U.S. Federal Aviation Administration (FAA) show that the internal short-circuit probability of 30kg overweight lithium batteries in transport vibration tests is 4.2 times that of 25kg compliant batteries—vibration can cause battery tab breakage and separator damage, directly triggering thermal runaway.

More dangerously, the “heat accumulation effect” of overweight lithium batteries significantly reduces safety margins. Lithium battery packs under 25kg can dissipate heat through ventilated packaging designs, while overweight batteries often adopt “tight stacking” to maximize capacity, trapping heat inside. Even normal operating heat from individual cells can trigger chain reactions of temperature rise. Tests by the China Academy of Civil Aviation Science and Technology found that a 40kg lithium battery pack left at 30℃ for 2 hours can reach an internal temperature of 58℃, approaching the critical temperature for electrolyte decomposition (60℃), making it highly susceptible to thermal runaway when exposed to minor external heat sources.

(2) Escalating Risk Severity: From “Local Incident” to “Systemic Disaster”

The harm caused by thermal runaway in overweight lithium batteries far exceeds the risk tolerance of air cargo. In terms of energy release, a fully burned 30kg lithium battery releases 15MJ of heat—equivalent to 4 liters of gasoline—capable of raising cargo hold temperatures to 800℃ in 3 minutes and melting aluminum alloy cargo hold walls; in contrast, the 12.5MJ heat from a 25kg lithium battery can be effectively controlled by cargo hold fire suppression systems. In the 2018 Qatar Airways A330 cargo plane accident, a fire caused by 35kg overweight lithium batteries breached the cargo hold firewall in 8 minutes, damaging the aircraft structure and resulting in 20 million US dollars in direct economic losses.

The risk of toxic gas leakage also multiplies with weight. Burning overweight lithium batteries release toxic gases such as hydrogen fluoride and carbon monoxide, with concentrations rising sharply as weight increases. FAA simulations show that 50kg lithium batteries produce hydrogen fluoride concentrations of 300ppm, far exceeding the human tolerance limit (1ppm). Even with cargo hold air filtration systems operating at full capacity, concentrations cannot be reduced to safe levels, potentially causing crew members to lose consciousness due to poisoning. Additionally, large amounts of toxic gases corrode aircraft electronic equipment, triggering secondary failures that further amplify accident consequences.

(3) Failure of Control Capabilities: “Dual Malfunction” in Fire Suppression and Emergency Response

Air cargo safety systems are designed around the 25kg critical limit, and overweight lithium batteries render these systems fully ineffective. For fire suppression, mainstream cargo planes equipped with Halon 1301 fire suppression systems have a design capacity of 18MJ, sufficient to cover heat release from 25kg lithium batteries but unable to handle sustained combustion of batteries over 30kg—after extinguishing agent depletion, fires quickly rekindle. In 2021, a FedEx cargo plane carrying 42kg overweight lithium batteries caught fire; crew members activated the fire suppression system three times but failed to control the blaze, eventually making an emergency landing at Memphis Airport.

In emergency response, overweight lithium batteries compress the “golden response time”. Aviation industry statistics show that 25kg lithium batteries take an average of 15 minutes from thermal runaway to full combustion, ample time for crews to complete the process of “confirming the fire, activating suppression, and coordinating an emergency landing”; for 35kg lithium batteries, this window shrinks to just 8 minutes, often leaving crews insufficient time for emergency procedures. More critically, overweight lithium battery packages exceed manual handling limits—when leakage or fire occurs, ground staff cannot quickly move the cargo, allowing risks to spread unchecked.

II. Unbearable Cost Black Hole: Soaring End-to-End Costs of Overweight Lithium Batteries

Beyond safety risks, overweight lithium batteries trigger cost 失控 across the entire air cargo chain. Costs surge in compliance, operations, and emergency response, trapping airlines and logistics companies in a “loss on every shipment” dilemma—another key driver behind rejections.

(1) Compliance Costs: From “Routine Declaration” to “Exorbitant Certification”

To transport overweight lithium batteries by air, enterprises first face prohibitive compliance barriers. Under International Civil Aviation Organization (ICAO) regulations, overweight lithium batteries require additional “special transport permit applications” and third-party “comprehensive risk assessments” covering 12 tests including thermal runaway simulation and packaging strength testing. Single-batch assessment costs range from 50,000 to 80,000 US dollars—over 10 times that of compliant batteries.

More critically, obtaining qualification to transport overweight lithium batteries incurs massive costs. Airlines must modify cargo holds by adding explosion-proof barriers and upgrading fire suppression systems, costing approximately 3 million US dollars per aircraft; simultaneously, crew members require specialized training in overweight lithium battery emergency response and toxic gas protection, at a cost of 20,000 US dollars per person. In 2022, a cargo airline attempted to obtain overweight lithium battery transport qualification, investing over 5 million US dollars upfront before abandoning the effort due to insufficient market demand.

(2) Operational Costs: From “Efficient Turnaround” to “Halved Efficiency”

Overweight lithium batteries significantly reduce air cargo operational efficiency and drive up unit transport costs. During loading, 25kg compliant lithium batteries can be quickly handled by one person, while batteries over 30kg require forklifts and other equipment, extending handling time from 2 minutes to 10 minutes per unit. This increases aircraft ground turnaround time by 1-2 hours. For a Boeing 747 cargo plane, each additional hour of ground time reduces daily flight frequency by one, resulting in 500,000 US dollars in lost daily revenue.

In terms of cargo hold utilization, the “weight-to-volume imbalance” of overweight lithium batteries wastes valuable space. To ensure flight safety, cargo holds must meet both weight and volume limits—overweight lithium batteries often exceed weight limits without filling available volume, preventing other cargo from being loaded. For example, a Boeing 777 cargo hold has a 50-ton weight capacity; loading 100 units of 30kg overweight lithium batteries (total 3 tons) does not reach the weight limit, but the space occupied could accommodate 5 tons of compliant cargo, directly costing the airline revenue from 2 tons of cargo.

(3) Risk Costs: From “Insurable Range” to “Insurance Vacuum”

The high-risk nature of overweight lithium batteries creates an “insurance dilemma”—difficult to insure and hard to claim—further increasing operational risk costs. Currently, major global insurers classify overweight lithium batteries as “high-risk cargo”, either refusing coverage or charging exorbitant premiums—typically 15%-20% of cargo value, 5-8 times that of compliant lithium batteries. In 2023, a logistics company attempting to insure a batch of 40kg overweight lithium batteries was quoted a premium of 25% of cargo value, ultimately abandoning transport due to cost concerns.

Even with insurance, claims face significant uncertainties. Insurers often deny payouts citing “failure to comply with aviation safety regulations”, leaving enterprises to bear losses alone in case of accidents. In 2021, a European logistics company’s 35kg overweight lithium batteries caught fire in transit, destroying 1 million US dollars worth of cargo in the aircraft hold; the insurer rejected the claim on grounds of “illegal overweight transport”, forcing the company to absorb all losses. Additionally, overweight lithium battery accidents may result in airline fines of up to 250,000 US dollars from regulators, further exacerbating cost pressures.

III. Conflict Between Industrial Demand and Aviation Regulations: The Underlying Tug-of-War Behind Rejections

Global air cargo’s rejection of overweight lithium batteries is not merely “safety obsession”, but a manifestation of tensions between the rapid development of the new energy industry and outdated aviation safety regulations. On one side are urgent demands from the electric vehicle and energy storage sectors for transporting large-capacity lithium batteries; on the other, the aviation industry’s uncompromising commitment to safety and cost 底线. This tug-of-war makes overweight lithium batteries a focal point of unresolvable conflict.

(1) “Transport Pain Points” of the New Energy Industry: Dual Demands for Efficiency and Cost

The rise of electric vehicles and energy storage has created massive demand for transporting overweight lithium batteries. A standard electric vehicle power battery weighs 60-100kg; splitting it into 3-4 packages to meet the 25kg limit not only increases packaging costs by 30%-50% but also reduces battery consistency and performance. A new energy vehicle enterprise calculated that splitting an 80kg battery for transport increases overall costs by 40%, adding over 200 million yuan in annual transport expenses.

Simultaneously, industry demands for transport speed conflict with aviation regulations. The “zero inventory” production models of new energy enterprises require rapid battery delivery, with air transport being the only option for intercontinental rapid shipping. Rejection due to overweight forces reliance on land or sea transport, extending delivery times from 3 days to 30 days and potentially halting production lines. In 2023, a European automotive factory shut down for two weeks after overweight lithium batteries were rejected by air cargo, resulting in 50 million euros in losses.

(2) “Bottom Line Adherence” of the Aviation Industry: Non-Negotiable Safety and Compliance

Faced with new energy industry demands, the aviation industry is not unwilling to compromise but cannot breach safety and cost 底线. From a safety perspective, the “zero-accident” goal of air transport tolerates no risks—an overweight lithium battery accident would not only cause massive economic losses but also destroy public trust in aviation safety, triggering an industry crisis. After the 2010 UPS Airlines Flight 6 crash, UPS’s air cargo volume plummeted by 30%, taking five years to recover.

From a cost perspective, retrofitting existing air transport systems for overweight lithium batteries requires massive investment with uncertain returns. Airlines would need to develop specialized cargo planes and build dedicated handling facilities to transport 100kg-class lithium batteries, potentially exceeding 1 billion US dollars in investment per company. With current demand for overweight lithium battery air transport remaining unstable, airlines fear inability to recoup investments and thus lack motivation to upgrade. An IATA survey showed that only 12% of airlines would consider modifying equipment to carry overweight lithium batteries, all requiring governments or enterprises to cover part of the costs.

(3) Regulators’ “Balancing Dilemma”: The Impossible Choice Between Regulation and Development

Regulators also face a dilemma between “safety supervision” and “industrial support”. On one hand, as guardians of aviation safety, regulators must strictly enforce the 25kg limit to prevent risk spread. The Civil Aviation Administration of China’s 2023 “Special Rectification Plan for Lithium Battery Air Transport Safety” explicitly mandates “zero tolerance” for overweight lithium batteries, with strict penalties for every violation. On the other hand, regulators must support new energy industry development and cannot completely block overweight lithium battery transport channels.

To resolve this impasse, some countries have launched “pilot breakthroughs”. For example, China initiated an “overweight lithium battery air transport pilot” at Shenzhen Airport, allowing compliant enterprises to carry lithium batteries under 30kg with specialized packaging and monitoring equipment; the EU relaxed weight limits to 35kg for low-risk new batteries such as solid-state batteries. However, these pilots are strictly limited in scope and conditions, unable to meet large-scale industrial demand, remaining “cautious exploration” rather than “full liberalization”.

IV. Breaking the Deadlock: Finding a New Balance Between Safety and Cost

Solving the overweight lithium battery air transport dilemma requires more than blanket rejection or blind weight limit relaxation. Instead, technological innovation, institutional optimization, and industrial collaboration must build a “safe, controllable, and cost-effective” new transport system, achieving win-win development for the new energy industry and aviation sector.

(1) Technological Innovation: From “Passive Protection” to “Active Prevention”

Technological breakthroughs are central to resolving conflicts. In battery technology, developing low-risk new batteries offers a fundamental solution. Solid-state batteries replace liquid electrolytes with solid alternatives, reducing thermal runaway risk by 80% compared to traditional lithium batteries while achieving higher energy density and lighter weight for the same capacity, naturally complying with the 25kg limit. Currently, enterprises like CATL and Panasonic have entered pilot production of solid-state batteries, with large-scale application expected by 2030—by then, overweight issues will be significantly alleviated.

In packaging technology, “intelligent explosion-proof packaging” can enhance overweight lithium battery safety. Equipped with temperature, pressure sensors, and automatic fire suppression systems, this packaging activates suppression within 0.5 seconds of detecting thermal runaway signs while transmitting real-time data to remote monitoring platforms via 5G. Tesla’s “35kg intelligent transport container” has passed ICAO testing, demonstrating higher safety than traditional 25kg packaging in pilots, promising to become a transitional solution for overweight lithium battery transport.

(2) Institutional Optimization: From “One-Size-Fits-All Weight Limits” to “Differentiated Supervision”

Refined regulatory policy adjustments can improve transport efficiency while ensuring safety. First, establish a “risk classification” supervision system, categorizing lithium battery transport risks as low, medium, or high based on battery type, condition, and packaging technology: relax limits to 40kg for low-risk solid-state batteries, maintain 25kg for medium-risk new liquid lithium batteries, and tighten to 10kg for high-risk used batteries, achieving “precision prevention”.

Second, implement “credit + technology” flexible supervision. Grant “overweight transport permits” to long-term compliant enterprises with strong technical capabilities, allowing them to carry lithium batteries under 30kg with specialized equipment and high-value insurance; simultaneously, establish a “blacklist” system to penalize non-compliant enterprises, forming a “trustworthy incentive, dishonest punishment” mechanism. Pilot data from Shenzhen, China shows this model achieved zero safety accidents while meeting 60% of industrial demand for overweight lithium battery transport.

(3) Industrial Collaboration: From “Siloed Efforts” to “Joint Innovation”

Deep collaboration between new energy enterprises and the aviation industry can reduce comprehensive transport costs for overweight lithium batteries. On one hand, joint R&D of “transport-friendly” batteries integrates air transport standards into battery design. For example, CATL and Boeing co-developed “modular power batteries” that flexibly split and combine to meet the 25kg limit for transport while enabling rapid assembly into large-capacity packs at destinations, balancing compliance and usability.

On the other hand, build “air-ground intermodal” logistics networks to reduce reliance on air transport alone. For domestic transport, adopt “drone + electric truck” short-haul intermodal models; for cross-border transport, establish hub networks of “nearby airports + land 接驳”, transporting overweight lithium batteries by land to airports in neighboring countries before splitting for air transport—complying with aviation regulations while shortening delivery times. In 2023, a Sino-German joint “Hamburg-Zhengzhou” air-ground intermodal route reduced cross-border transport time for overweight lithium batteries from 30 days to 7 days, cutting costs by 20%.

Conclusion

Global air cargo’s rejection of overweight lithium batteries is a rational choice under dual constraints of safety and cost, not an industry barrier. This phenomenon exposes mismatches between the rapid development of the new energy industry and traditional aviation safety systems, while forcing all stakeholders to seek more scientific solutions. From technological innovation to institutional optimization, and industrial collaboration to regulatory upgrading, paths to resolving the overweight lithium battery transport dilemma are increasingly clear—the key lies in abandoning “either/or” thinking and reducing compliance costs while improving efficiency through systemic reform, without compromising safety. When new battery technologies mature, regulatory systems improve, and collaborative networks take shape, overweight lithium batteries may no longer be “taboo” for air cargo but rather a new growth driver for integrated development of new energy and aviation industries. Until then, upholding the 25kg limit and rejecting overweight shipments remains the aviation industry’s most responsible balance between safety and cost.