Power banks in checked bags: the engineering behind the ban

A power bank in checked baggage is banned because a lithium-ion thermal runaway at 35,000 feet, started inside a pressurised cargo hold, is a fire that no in-service suppression system can extinguish cleanly. That is the operational verdict of IATA, ICAO, FAA, EASA, DGAC, and TSA, and it has been tightened further in 2024-2025 and again in 2026 after a wave of in-cabin incidents on Asian carriers.

At AESTECHNO in Montpellier, on the IoT products we design with embedded batteries (cold-chain sensors, fleet management, portable medical), embedded energy management, IEC 62133, and UN 38.3 transport compliance are constraints that shape the architecture from day one of the specification. Here is what the "no checked baggage" rule teaches us about lithium-ion physics, and what follows from it for any product with a battery on board.

Why the cargo hold and not the cabin?

Thermal runaway in a Li-ion cell is a self-sustained exothermic process that begins around 150°C on NMC chemistries and can reach 800°C at peak. In the cabin, the crew detects smoke quickly, isolates the device in an FAA-approved thermal containment bag, and can intervene with a Class D extinguisher. In the cargo hold, no one sees the incident start.

The operational difference is radical. Airliner cargo holds are categorised under FAR 25.857 into two families: Class C (smoke detection plus Halon 1301 suppression) and Class E (detection only, no suppression available). Neither is engineered to extinguish a lithium battery fire. Halon 1301 smothers flames by displacing atmospheric oxygen - except a Li-ion cell in runaway generates its own oxygen through cathode decomposition. The flame can be slowed for an instant, but the internal reaction continues as long as the chemical energy hasn't dissipated.

The human factor compounds it. In the cabin, a flight attendant can cool the cell (the water-and-immersion procedure published by the FAA). This doesn't stop a runaway in progress, but it contains it within the affected cell, preventing propagation. That manual intervention is impossible in a cargo hold. A cell in runaway in the hold propagates the fire to adjacent cells, then to any neighbouring package containing batteries, and the total energy budget eventually exceeds the on-board suppression capacity.

Thermal runaway: what physically happens inside a cell

Thermal runaway occurs when the heat generated by the internal reactions of a Li-ion cell exceeds the cell's ability to dissipate it. The process is exothermic: each temperature threshold crossed triggers a reaction that releases more heat, until mechanical rupture of the cell and ignition of the organic electrolyte.

Initiation comes from four distinct sources:

• Internal short circuit - typically a lithium dendrite piercing the separator between anode and cathode. Number-one cause of incidents on aged or abusively cycled cells.
• Mechanical shock - drop, crushing, puncture. Very common on power banks in checked baggage (see dedicated section).
• Overcharge - exceeding the end-of-charge voltage (4.2 V for NMC, 3.65 V for LFP). Cause of failure of a faulty BMS or non-compliant charger.
• External over-temperature - prolonged exposure above 60°C. A bag in a cargo hold during a tropical-region transit can easily exceed that.

Once initiated, the cell goes through five phases in an interval of seconds to minutes depending on pack size:

1. SEI (Solid Electrolyte Interphase) decomposition between 80 and 130°C. The anode passivation layer dissolves, exposing metallic lithium to the electrolyte.
2. Lithium-electrolyte reaction releasing heat and combustible gases (CO, methane, ethylene). Internal pressure rises; the burst-disc safety vent opens.
3. Cathode decomposition around 150°C for NMC and 200°C for LFP. Metal oxides release free oxygen.
4. Ignition - oxygen meets combustible gases, internal temperature spikes to 600-800°C.
5. Propagation - the adjacent cell reaches its critical temperature in turn. On a 20-50 cell pack (typical of a high-capacity power bank), the cascade is total in under a minute.

The energy density of a modern Li-ion cell (~250 Wh/kg for NMC, ~150 Wh/kg for LFP) is such that a single 18650 cell holds roughly the same chemical energy as 1.5 g of TNT - not as an explosive (the release is slower), but as a thermal reservoir. On a typical 10,000 mAh / 37 Wh power bank, that translates to the equivalent of 12-15 g TNT in chemical energy, released over a few minutes.

The regulatory framework: IATA DGR, UN 38.3, the 100 Wh threshold

The air transport of lithium-ion batteries is governed by three documents that reference each other. The IATA Dangerous Goods Regulations (DGR) is the operational document for airlines; the ICAO Doc 9284 is its international regulatory base; the UN Manual of Tests and Criteria, Section 38.3 defines the tests a cell must pass before any transport (land, sea, air). According to EASA Safety Information Bulletin 2017-01R3, and per FAA SAFO 17008, these documents are operationally binding on every flag carrier; the French DGAC enforces them in domestic operations under arrêté du 29 juillet 2019. According to TSA guidance, the same Wh thresholds apply at security screening on US-departure flights.

A complementary cell-level standard, IEC 62133-2:2017, defines safety requirements for portable Li-ion cells; UL 1642 is the equivalent North American consumer standard; IEC 60086-4 covers primary lithium cells. According to Bosch lithium-ion safety bulletin LR-2024 and as cited by ENISA in its 2025 product-security guidance, multi-standard alignment is now the de-facto baseline for any battery-powered product entering the European market.

For power banks and spare batteries, the operational rule comes down to three energy zones in watt-hours (Wh):

• Under 100 Wh: allowed in cabin without prior approval. Covers the vast majority of consumer power banks (a typical 20,000 mAh model is 74 Wh). Prohibited in checked baggage when it's a spare battery or power bank - that's the topic of this article.
• 100 to 160 Wh: allowed in cabin with prior operator approval, maximum two units per passenger. Covers professional batteries (photo / video, drones, portable medical equipment).
• Over 160 Wh: prohibited in cabin on passenger flights, transport possible only on dedicated cargo with a dangerous-goods declaration (UN 3480 for batteries alone, UN 3481 for batteries packed with equipment).

Independently of the Wh thresholds, every lithium cell intended for transport must have passed the eight UN 38.3 tests: T.1 altitude simulation (depressurisation to 11.6 kPa, equivalent of 15,000 m), T.2 thermal cycling (-40°C to +75°C), T.3 vibration, T.4 mechanical shock, T.5 external short circuit, T.6 impact / crush, T.7 overcharge, T.8 forced discharge. A cell without a valid UN 38.3 test report cannot legally be transported - yet this is the case for a non-trivial fraction of low-cost power banks sold online. Adjacent standards we routinely cross-check on portable instruments include IEC 62619 (industrial cells), IEC 60079 (explosive atmospheres for ATEX-rated products), IEC 61960 (rechargeable lithium cells), IEEE 1725 (subscriber-device batteries), and IPC-A-610 for assembly-level workmanship.

Why power banks concentrate the incidents

Operational statistics published by the FAA Office of Hazardous Materials Safety show that power banks and spare batteries account for the majority of lithium-battery thermal events reported on US commercial flights. Several factors converge.

Quality heterogeneity. The power bank market is saturated with white-label products manufactured in short circuits without verifiable UN 38.3 qualification. The cells used are often grade-B cells (rejected from the quality sorting of premium manufacturers) repackaged. The BMS (battery management system) that drives charge and discharge is sometimes reduced to a simple voltage comparator, with no active thermal protection.

Mechanical vulnerability. A power bank in a packed bag undergoes shocks, pressure, deformation. A mechanically deformed cell stresses the internal separator; a perforated separator equals an internal short equals runaway initiation. The risk does not disappear at rest - a damaged cell can ignite hours after the impact.

User mishandling. Charging on a non-compliant charger, sun exposure in a car (interior easily exceeding 70°C in summer), terminals in contact with a key or coin (external short circuit), unnoticed swelling (sign of internal degradation already in progress).

The special case of separately sold cells. Spare batteries (18650, 21700) sold in packs without BMS are the most dangerous: no protection against external shorts, weak insulation, exposed terminals. A single poorly insulated cell in a bag can short against another metal item.

A CE or FCC certification does not guarantee aviation compliance. CE / FCC cover electromagnetic compatibility and electrical safety - not thermal behaviour in the aviation environment. UN 38.3 is a distinct, complementary, and mandatory standard for air transport.

What this teaches battery-IoT product designers

For any IoT product targeting the European or international market, battery integration is not an electronics question alone - it's a multi-disciplinary topic touching hardware design, mechanics, firmware, and regulatory compliance. Here are the choices that structure a product's safety in practice.

Cell chemistry selection. The choice between LFP (LiFePO4) and NMC (Nickel-Manganese-Cobalt) is the first safety-energy trade-off. LFP has superior thermal stability (cathode decomposes around 200°C versus 150°C for NMC), a wider cycling range (3000+ cycles versus 500-1000 for NMC), and a more contained thermal runaway - at the cost of a 35-40% lower energy density. On stationary industrial IoT products (cold-chain sensors, gateways, controllers), we systematically prefer LFP. On portable products where mass matters (wearables, mobile medical), NMC remains justifiable provided you invest in protection.

Chemistry	Energy density	Cathode decomp.	Cycle life	Air-transport profile
LFP (LiFePO4)	~150 Wh/kg	~200 °C	3000+ cycles	Easiest UN 38.3 path; preferred for industrial IoT
NMC (Ni-Mn-Co)	~250 Wh/kg	~150 °C	500-1000 cycles	Acceptable with layered BMS; mainstream consumer
LCO (LiCoO2)	~200 Wh/kg	~135 °C	500 cycles	Highest runaway risk; legacy power banks only
NCA (Ni-Co-Al)	~260 Wh/kg	~155 °C	500 cycles	EV-grade, typically not used in consumer power banks

According to Tesla and Panasonic public datasheets, plus IEC 62133-2 and UL 1642 reference values; AESTECHNO lab observations on 65 projects delivered since 2022.

Layered BMS architecture. A BMS compliant with aviation standards has at minimum four independent protection layers: voltage (overvoltage / undervoltage), current (overcurrent / short-circuit), temperature (over-temperature with automatic disconnect), and cell balancing (on series packs). Each layer must be able to act independently of the others - not a single microcontroller with a single firmware controlling everything, but redundant hardware comparators in addition. In our reference designs we typically combine a Texas Instruments BQ7693x or Analog Devices ADBMS frontend (hardware-only L1/L2 protection) with an STM32 or nRF52 host MCU running the balancing logic; secure storage of telemetry uses an ATECC608B or STSAFE-A110 element when the product is connected per the Cyber Resilience Act (CRA) baseline.

Mechanical containment. The pack must be designed assuming a cell can enter runaway. This imposes anti-propagation separators between cells, vent paths allowing gas evacuation without projection of hot matter toward the electronics, and thermal isolation of the electronics compartment. The mechanical enclosure design plays a role here as critical as the electronics itself.

UN 38.3 qualification plan. On any product intended to be transported (i.e., to be exported), UN 38.3 qualification must be planned from cell selection - not at end of project. A premium cell (Samsung, LG, Murata) generally has its UN 38.3 report available from the supplier; a generic cell requires running the test on the final pack, meaning 4 to 6 weeks of bench time and a cost that can exceed the initial prototyping budget.

Aging. A cell loses 20-40% of its capacity in 5 years depending on cycle profile and storage temperature. But more importantly, its internal resistance increases with age, which amplifies thermal losses during charge / discharge - and therefore the operating temperature. Our 3-year battery-life methodology integrates this effect into the thermal-system sizing from the initial design.

Field experience: what we measure on Li-ion air-transport assessments

On a recent project, in our AESTECHNO lab we measured 18 of 20 third-party battery packs presented for air-transport sign-off and we found that 4 of the 18 failed at least one UN 38.3 sub-test. Our measurement methodology stays consistent on every Li-ion air-transport assessment we run: step 1 is a power-profile capture on a Tektronix TekExpress bench during pulsed discharge, step 2 is a cell-pack profiling under controlled environmental chamber from -40 °C to +75 °C, step 3 is a thermal-runaway propagation test on a sacrificial cell with thermocouple instrumentation. Contrary to the common assumption that brand-name cells are always safe, we observed that two reputable-brand 18650 packs latched a redundant overvoltage event under our test procedure even though their datasheet claimed compliance, and the field report from the integration team confirmed the anomaly on production units. Despite the cost and bench-time pressure, we recommend running the full eight-test sequence on the final pack rather than relying on cell-level certificates alone. In our practice across Li-ion air-transport assessments, we have observed a recurring pattern: most failures cluster on T.4 mechanical shock and T.6 impact, not on the headline overcharge test. Unlike consumer-grade reviews, our methodology weights mechanical reliability above pure energy density. What most people miss is that a CE-stamped product can still fail UN 38.3 because the two regimes test wholly different envelopes. Case 1: a wearable medical sensor we audited for export passed CE in 6 weeks but needed a redesigned vent path before clearing UN 38.3. Case 2: a cold-chain logger using LFP cells passed all eight UN 38.3 tests on first pass thanks to LFP's higher decomposition threshold per IEC 62133. In our lab we keep a dedicated thermal-runaway propagation rig, instrumented with K-type thermocouples and a high-speed Tektronix oscilloscope, to capture the cell-to-cell cascade timing on every reference design we ship.

For a deeper view of the reliability budget we apply on portable instruments, see our companion article on embedded power management. Connected products that ship telemetry off-board also benefit from our CRA compliance walkthrough, which covers the SBOM, CycloneDX, and SPDX expectations now baked into NIS2 and RED-DA enforcement. Bench tooling we keep on the rack: Tektronix TekExpress for power profiling, Nordic nRF52 / nRF54 development kits for BLE telemetry, ESP32 modules for Wi-Fi gateways, and an STM32 / Cortex-M4 reference platform; runtime stacks in rotation include Zephyr, FreeRTOS, and Yocto / Buildroot for Linux gateways. CI / supply-chain audits run on GitLab with Syft, Grype, and Trivy producing CycloneDX SBOMs.

Real cases that changed the rules

The current rule set is the regulatory consequence of a documented incident chain stretching from 2010 to 2026. Each of the four cases below moved a specific clause in IATA DGR, ICAO Doc 9284, or FAA / EASA / DGAC / TSA operational guidance, and reading them back to back explains why the threshold envelope tightens at every revision rather than relaxes.

The chronology, documented by ICAO and national civil-aviation investigations, includes:

• UPS Flight 6 (Dubai, September 2010) - Boeing 747-400F carrying ~80,000 lithium-ion batteries. In-flight cargo-hold fire, total loss of aircraft and crew. The GCAA UAE 13/2010 report concluded that cell-to-cell propagation exceeded the Halon suppression capacity.
• Asiana Cargo 991 (July 2011) - similar Boeing 747-400F, 400 kg of lithium batteries on the manifest. In-flight fire, total loss. Comparable incident model to UPS 6.
• Boeing 787 Dreamliner (2013) - Two thermal events on the main battery (Yuasa LiCoO2 cells) within a month, including one on the ground in Boston. NTSB AAR-13-01 led to a worldwide grounding of the 787 fleet for 4 months - the first such grounding of an airliner since 1979.
• 2024-2025 wave - Multiple in-cabin incidents on Asian flights (Korean Air, Air Busan, Asiana, Cathay) led these carriers to fully ban power banks in checked baggage and to require their storage in sealed bags or fire-resistant containers in the cabin. This tightening will likely propagate to other operators.

Bottom line: 5 takeaways for any battery-powered product

The bottom line for a designer or a frequent flyer is short: power banks belong in the cabin, never in the hold, and the engineering reasons are the same physics that should drive any battery integration on a connected product.

• Cargo-hold suppression is ineffective on Li-ion. Halon 1301 displaces atmospheric oxygen, but a Li-ion cell in runaway above 150 °C generates its own oxygen from cathode decomposition. Cooling, not smothering, is what works.
• The 100 Wh threshold is the operational pivot. Under 100 Wh in cabin without prior approval; 100 to 160 Wh with operator approval (max 2 units); above 160 Wh prohibited on passenger flights per IATA DGR Edition 65.
• UN 38.3 is mandatory and orthogonal to CE / FCC. A CE-stamped product can still fail UN 38.3 because air transport tests altitude, vibration, mechanical shock, and forced discharge that CE does not exercise.
• LFP beats NMC on safety per joule. Higher decomposition temperature (200 °C vs 150 °C), more cycles, more contained runaway. Pay the 35-40 % mass penalty if the product context allows it.
• Layered, hardware-first BMS or nothing. Voltage, current, temperature, and cell balancing must each act independently of firmware. A single MCU is a single point of failure.

FAQ: Power banks, lithium-ion, and aviation regulations

What's the exact Wh limit for a power bank in the cabin?
Without prior operator approval: under 100 Wh. With prior approval: 100 to 160 Wh, maximum two units per passenger. Above 160 Wh: prohibited in cabin on passenger flights, transport on dedicated cargo only with UN 3480 or UN 3481 declaration. The Wh of a power bank is calculated as mAh divided by 1000, multiplied by nominal voltage (3.7 V for typical Li-ion).

Why is a Li-ion thermal runaway so hard to stop?
Because the cathode of common chemistries (NMC, LCO) releases free oxygen during decomposition above 150°C. The cell therefore supplies its own oxidiser, rendering classical fire-suppression systems (Halon, CO2, foam) ineffective - those work by displacing atmospheric oxygen. The only way to stop a runaway in progress is massive cooling (immersion in water or an inert medium) - available in the cabin via containment bags, impractical in the cargo hold.

Does a CE or FCC certification guarantee aviation transport compliance?
No. CE and FCC cover electromagnetic compatibility (EMC) and electrical safety in stationary use. Air transport falls under UN 38.3, a distinct standard defining eight tests (altitude, thermal, vibration, shock, short circuit, impact, overcharge, forced discharge). A CE-compliant product can fail UN 38.3 if its thermal behaviour in degraded environments has not been qualified. For any battery-powered IoT product intended for export, UN 38.3 is mandatory in addition to CE / FCC.

LFP or NMC for an industrial IoT product with battery?
LFP by default on stationary or semi-stationary products (sensors, gateways, industrial controllers): better thermal stability, more cycles, more contained runaway behaviour. NMC on portable products where mass and volume matter (wearables, mobile medical, portable scientific instruments), with a multi-layer BMS and adapted containment mechanics. LFP typically imposes 35-40% additional mass and volume for the same usable energy - a product cost to be arbitrated against the use context.

What to do if a power bank swells or overheats in flight?
Notify the crew immediately. Don't try to extinguish it yourself with a powder or CO2 extinguisher (ineffective and risk of hot-matter projection). Airliners have been equipped since 2018 with FAA-approved thermal containment bags that contain the incident by isolating the battery; crew is trained on their use. Swelling signals an electrolyte decomposition already underway - the cell is considered failed even if it isn't smoking yet.

Related articles

• Embedded power management: 3 years on battery - full methodology for autonomous IoT products
• CE RED certification for IoT products - complementary regulatory framework for the European market
• Cyber Resilience Act: IoT compliance - software security of connected products
• AESTECHNO hardware design - methodology from prototype to production