Lithium battery rules for flying

Why lithium batteries are regulated

Lithium-ion and lithium-metal batteries can enter a condition called thermal runaway — an uncontrolled, self-sustaining exothermic reaction triggered by overheating, short-circuit, physical damage, or manufacturing defects. During thermal runaway, a battery generates heat faster than it can dissipate it, leading to fire, the release of toxic gases, and potential explosion.

In the aircraft cabin, crew can detect and respond to a battery fire within seconds using halon extinguishers or water. In the unpressurised, inaccessible hold, a fire may go undetected until it has spread. This asymmetry of response capability explains why spare batteries are banned from the hold but permitted in the cabin.

The Federal Aviation Administration (FAA) maintains a database of aviation incidents involving lithium batteries. As of 2024, the FAA records over 400 confirmed smoke, fire, or explosion events attributable to lithium batteries on commercial aircraft.

Wh ratings explained

Battery capacity for aviation purposes is expressed in watt-hours (Wh). The watt-hour rating indicates the total energy a battery can store. Most consumer devices print the Wh rating on the battery label. If only voltage (V) and milliamp-hours (mAh) are printed, use this formula:

Some manufacturers print the rated capacity in mAh based on the USB output voltage (5 V) rather than the cell voltage (3.6–3.7 V). This inflates the apparent mAh figure. For aviation compliance, use the cell voltage when calculating Wh. When in doubt, check the manufacturer's specification sheet or the label on the battery itself.

Wh thresholds and what they mean

All spare batteries must be in carry-on regardless of Wh rating. Batteries installed in devices may travel in checked baggage (subject to airline policy), but spare cells may not.

Spare batteries and power banks

A spare battery is any lithium cell or battery not currently installed in a device. Power banks fall into this category — they are treated identically to spare batteries under IATA DGR. Both must travel in carry-on baggage only.

Terminal protection is required for all spare batteries to prevent short-circuit. Acceptable protection methods include:

• Individual plastic cases or original retail packaging.
• Placing each battery in a separate sealed plastic bag.
• Covering terminals with tape.

Loose batteries rattling together in a bag are not compliant and can short-circuit, causing a fire risk. Battery compartments on devices should be secured; batteries with damaged casings or exposed wiring must not be transported.

Common device types and their typical ratings

Damaged and recalled batteries

Batteries that are swollen, cracked, leaking, or show signs of damage must not be transported on any aircraft. A battery subject to a manufacturer recall is similarly prohibited; the recall may indicate a manufacturing defect that makes thermal runaway more likely.

Airlines and security authorities do not have a systematic method for identifying recalled batteries at the checkpoint. Responsibility for compliance rests with the passenger. The US Consumer Product Safety Commission (CPSC) and the UK Office for Product Safety and Standards (OPSS) maintain online recall databases.

Airline comparison

The following table reflects each airline's published lithium battery policy as of early 2025. All major carriers follow IATA DGR as a minimum. Policies are subject to change; always verify on the airline's website before travel.

Source: individual airline dangerous goods policies; IATA DGR Packing Instructions 965–970 (current edition).