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Lithium-ion batteries catch fire when a fault starts a rapid rise in cell temperature and the heat drives further chemical reactions that produce still more heat. This self-accelerating failure is called thermal runaway. It can begin in one cell, spread to other cells in a battery pack, and ignite nearby materials. It is a possible failure mode—not a sign that every lithium-ion battery is about to catch fire.
What happens inside a lithium-ion battery?
In normal use, lithium ions move between a cell’s electrodes through an electrolyte, while electrons flow through an external circuit to power a device. A thin separator keeps the electrodes apart while allowing ions to pass. If the electrodes make contact, an internal short circuit can result.
Damage, a manufacturing defect, overheating, overcharging, or another fault can trigger a short or otherwise raise a cell’s temperature. Heat can then drive exothermic reactions inside the cell. Those reactions release more heat and can raise pressure. If heat is generated faster than it can escape, the temperature continues climbing: that feedback loop is thermal runaway. Separator failure can worsen the short, and the cell may vent hot gases or ignite.
How can one failing cell involve a whole battery pack?
A cell is an individual electrochemical unit; a pack contains one or more cells connected and packaged together. Thermal runaway begins at the cell level, but heat from a failing cell can raise the temperature of neighboring cells until they fail as well. That cell-to-cell spread can turn a single-cell fault into a pack fire. The pack may also involve its casing, device, packaging, or other nearby combustible materials.
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These are distinct parts of an incident: the original fault may start in one cell, heat may propagate through a pack, and flames may then ignite materials outside it. A pack fire does not establish that every cell failed in the same way, and the specific cause of an incident requires investigation.
What can cause a lithium-ion battery to overheat or fail?
Recognized risk conditions include physical damage, short circuits, overheating, overcharging, exposure to water, manufacturing defects, and improper packing or handling. These are possible initiating conditions, not a checklist that identifies the cause of any particular fire.
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In one investigated example, the National Transportation Safety Board determined that a short circuit between a terminal bolt and upper cells caused thermal runaway in a 2016 FedEx truck incident. It also identified a design that did not protect against short-circuiting and combustible packaging as contributing factors. That finding describes that incident; it does not show that every battery fire has the same cause.
What should you do if a phone battery is swelling or a battery is smoking?
Swelling, unusual heat, smoke, or burning are warning signs. Prioritize getting away from the battery and follow local emergency guidance. Do not pick up a battery that is overheating, smoking, or burning, or try to transport it as though it were safe. If it is burning or creating an immediate danger, contact emergency services.
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There is no universal household firefighting procedure established by the cited agency guidance. A response discussed by the NTSB for a vessel and its crew is specific to that incident and setting; it should not be treated as do-it-yourself instructions for a home, vehicle, or consumer device. Keep people clear and rely on emergency responders for a dangerous fire.
How can you reduce the risk?
- Follow the device and battery manufacturer’s care, charging, and maintenance instructions.
- Avoid charging unattended, and keep batteries and chargers away from heat sources and flammable materials.
- Stop using a battery or device that is damaged or behaving abnormally; do not attempt to keep charging it.
- Dispose of damaged batteries properly rather than placing them in ordinary household waste. Follow local battery-disposal guidance.
- When choosing a device or battery, check whether it is certified by Underwriters Laboratories or another recognized organization. Certification is useful information, not a guarantee that failure is impossible.
Can you bring a power bank on a plane?
Under FAA guidance, spare, uninstalled lithium-ion batteries—including power banks—must be carried in carry-on baggage, not checked baggage. If a carry-on bag is checked at the gate or planeside, remove spare batteries and power banks and keep them in the cabin. Damaged or recalled batteries likely to spark or generate dangerous heat must not be carried aboard in carry-on or checked baggage unless they have been removed or otherwise made safe.
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Rules can depend on the battery, device, and trip. Check the FAA’s current battery guidance and your airline’s instructions, including the applicable watt-hour limits, before traveling. If a battery or device overheats, swells, smokes, or burns on an aircraft, notify the crew immediately; passengers should not try to manage the incident on their own.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How common are lithium-ion battery fires?
National Institute of Standards and Technology (NIST) estimates published in 2026 put the number of structure fires involving lithium-ion batteries since 2011 at 198,000, with a 95% confidence interval of 84,000 to 465,000. NIST also estimated 5,718 electric-vehicle and plug-in-hybrid fires since 2011, with a 95% confidence interval of 2,866 to 10,846.
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These are estimates from a multi-source analysis, not complete official counts. NIST notes that source data are fragmented and incomplete, and that some datasets make lithium-ion battery fires difficult to identify. The figures provide context, not a precise tally of every incident.
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