Yes, all lithium batteries are classified as hazardous materials when being transported, no matter the size or quantity. The U.S. Department of Transportation designates them as Class 9 hazardous materials, a category for miscellaneous dangerous goods. This applies to the tiny cell in a hearing aid, the rechargeable pack in your laptop, and every size in between.
Why Lithium Batteries Are Classified as Hazmat
Unlike standard alkaline batteries, most lithium batteries contain a flammable electrolyte and pack an extremely high energy density into a small package. That combination creates both chemical and electrical hazards. The flammable electrolyte can leak or release flammable gases when the battery is exposed to high temperatures or physical damage. The high energy density means a failure can release a lot of heat very quickly.
The specific danger regulators worry about is called thermal runaway: an uncontrolled chain reaction of heating inside the battery that can lead to fire or explosion. Thermal runaway can be triggered by a short circuit, overcharging, or mechanical damage like a puncture or hard drop. Once it starts in one cell, it can spread to neighboring cells, which is why a single damaged battery in a cargo hold full of packages is such a serious concern. These risks are what earned lithium batteries their hazmat classification, and they apply to both rechargeable (lithium-ion) and non-rechargeable (lithium metal) types.
What This Means for Shipping
If you’re shipping lithium batteries by ground, air, or sea, federal regulations require specific packaging, labeling, and documentation. Packages containing lithium batteries generally need a Class 9 hazard label and lithium battery handling marks. The exact requirements depend on whether the batteries are shipped by themselves, packed alongside a device, or already installed in equipment.
Air transport has the strictest rules. The International Air Transport Association (IATA) requires that lithium-ion cells and batteries shipped by themselves be charged to no more than 30% of their rated capacity. Starting in 2026, batteries packed alongside equipment will also need to meet that 30% charge limit. Lithium-ion batteries shipped on their own are completely forbidden as cargo on passenger aircraft and can only move on cargo-only flights.
The penalties for getting this wrong are steep. PHMSA, the federal agency that enforces hazmat shipping rules, can issue civil fines up to $78,376 for a knowing violation. If a violation results in death, serious injury, or substantial property destruction, the maximum jumps to $182,877. Even a minor training-related violation carries a minimum penalty of $471.
Rules for Air Travelers
For passengers, the rules are more forgiving but still specific. Devices with lithium batteries installed (phones, laptops, cameras) can go in either carry-on or checked bags. Spare batteries and portable power banks are a different story: they must go in your carry-on, never in checked luggage. If your carry-on gets gate-checked, you need to pull out any spare batteries and power banks and bring them into the cabin with you.
Size limits apply to what you can bring aboard:
- Lithium-ion (rechargeable): Up to 100 watt hours per battery with no quantity limit, as long as they’re for personal use. With airline approval, you can also carry up to two larger spare batteries rated between 101 and 160 watt hours each.
- Lithium metal (non-rechargeable): Up to 2 grams of lithium per battery with no quantity limit. With airline approval, up to two spare batteries containing between 2 and 8 grams of lithium.
For reference, most phone batteries fall well under 20 watt hours and laptop batteries typically range from 50 to 100 watt hours, so the average traveler won’t run into these limits. Batteries carried for resale or as vendor samples are prohibited entirely on passenger flights.
Small Batteries Still Count
A common misconception is that small lithium batteries, like the ones in a watch or a single AA-size lithium cell, aren’t really hazmat. Legally, they are. The PHMSA guide is explicit: all lithium cells and batteries are hazardous materials when being transported, no matter the size or quantity. However, smaller batteries that meet certain thresholds can qualify for reduced shipping requirements, sometimes called “excepted” provisions. These batteries still need proper packaging and marking, but the paperwork and labeling burden is lighter than for fully regulated shipments.
The distinction between “excepted” and “fully regulated” often confuses people into thinking small batteries aren’t hazmat at all. They are. The regulations simply allow a streamlined process for lower-risk shipments because the consequences of a failure in a single coin cell are very different from those in a pallet of large battery packs.
Damaged or Recalled Batteries
Batteries that are damaged, defective, or under recall pose an elevated risk and face additional restrictions. A battery with a cracked casing, one that has been swelling, or one that feels unusually hot has a much higher chance of entering thermal runaway during transport. These batteries generally cannot be shipped using the standard exceptions available to small or low-risk batteries. They typically require approval from the relevant authority, specialized packaging designed to contain a potential fire, and in some cases can only move by ground transportation.
Signs that a lithium battery may be compromised include visible cracking or denting, unusual heat during charging or use, swelling of the battery casing, and a chemical or burning smell. If you need to return or dispose of a battery in this condition, contact the manufacturer or a local hazardous waste facility rather than dropping it in the mail.