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Understanding the Risks of Thermal Runaway

  //travel-leisure.news-articles.net/content/2026/ .. /understanding-the-risks-of-thermal-runaway.html
  Published in Travel and Leisure on Sunday, April 26th 2026 at 14:23 GMT by Travel + Leisure
      Locale: UNITED STATES

The Science of the Danger: Thermal Runaway

The primary reason aviation authorities, such as the Federal Aviation Administration (FAA) and the Transportation Security Administration (TSA), strictly regulate lithium batteries is a phenomenon known as "thermal runaway." Lithium-ion batteries are highly energy-dense, which makes them efficient but also potentially volatile. If a battery is damaged, short-circuited, or exposed to extreme temperatures, it can enter a self-sustaining cycle of heating.

Once thermal runaway begins, the battery releases energy in the form of intense heat, which can ignite nearby flammable materials. In the confined space of an aircraft, a battery fire is particularly dangerous because it is difficult to extinguish and can release toxic gases. This is the central reason why the location of the battery during transit is so heavily scrutinized.

Carry-On vs. Checked Luggage

The most critical rule for any traveler is the placement of spare lithium batteries. Spare batteries--including portable power banks and loose cells--are strictly prohibited in checked luggage. They must be carried in the cabin (carry-on luggage).

The reasoning behind this is simple: accessibility. If a battery catches fire in the passenger cabin, flight attendants and passengers are equipped and positioned to respond immediately using on-board fire extinguishers. Conversely, a fire starting in the cargo hold is far more dangerous, as it may go undetected for several minutes and is much harder to combat effectively while the plane is at cruising altitude.

Understanding Battery Capacity (Watt-Hours)

Not all lithium batteries are treated equally; the level of restriction often depends on the battery's capacity, measured in Watt-hours (Wh).

1. Under 100 Wh: Most consumer electronics, including standard smartphones and laptops, fall into this category. These are generally permitted in carry-on luggage without prior airline approval.
2. 100 to 160 Wh: Larger batteries, often found in professional photography gear or high-capacity power stations, fall into this middle tier. These typically require explicit approval from the airline before the passenger is allowed to board.
3. Over 160 Wh: Batteries exceeding this limit are generally prohibited from passenger aircraft entirely and must be shipped as hazardous cargo via specialized freight services.

Integrated vs. Spare Batteries

There is a nuance regarding batteries that are integrated into a device versus those that are loose. A device with a built-in battery (like a laptop or camera) is generally permitted in checked luggage, provided the device is completely powered down and protected from accidental activation. However, safety experts and airlines still strongly recommend keeping these devices in the cabin to ensure they can be monitored.

Critical Guidelines for Lithium Battery Transport

To ensure safety and avoid confiscation at security checkpoints, travelers should adhere to the following protocols:

• Strictly forbid spare batteries in checked bags: Power banks and loose lithium batteries must always be in carry-on luggage.
• Protect terminals: To prevent short-circuiting, spare battery terminals should be covered with electrical tape or placed in individual plastic bags/protective pouches.
• Power down devices: Any electronic device placed in checked luggage must be completely off, not in "sleep" or "standby" mode.
• Verify capacity: Check the label of power banks to ensure they are under 100 Wh; if they are not, contact the airline in advance.
• Avoid damage: Never travel with batteries that show signs of swelling, leaking, or physical damage, as these are high-risk candidates for thermal runaway.