Lithium batteries are one of the fastest-growing hazmat categories on the road, because they are in everything from phones to power tools to vehicles. They are regulated for a simple reason: when they fail, they can overheat and catch fire in a way that is hard to extinguish. The rules reflect that risk and keep evolving.
This is study guidance, not regulatory advice. The binding rules are in 49 CFR 173.185 and your official state CDL manual.
Why they are regulated
Lithium batteries can undergo thermal runaway, a self-feeding overheating that leads to fire. Because a damaged, defective, or improperly packed battery can ignite, transport rules control how they are packaged, marked, and shipped. They are generally classed as Class 9 miscellaneous, since their hazard does not fit the earlier classes.
The UN numbers and marking
Lithium batteries are identified by specific four-digit identification numbers, and they carry a dedicated lithium battery mark.
| UN number | What it covers |
|---|---|
| UN3480 | Lithium ion batteries (shipped alone) |
| UN3481 | Lithium ion packed with or in equipment |
| UN3090 | Lithium metal batteries (shipped alone) |
| UN3091 | Lithium metal packed with or in equipment |
The lithium battery mark is one of the special package markings that identifies these shipments, separate from the hazard-class placard.
Damaged and defective batteries
Batteries that are damaged or defective get stricter treatment, because they are the most likely to fail. There are specific rules for handling and packaging them, and some damaged batteries are restricted from certain transport entirely. PHMSA maintains dedicated guidance on transporting lithium batteries.
Where it fits
Lithium batteries are a live, evolving area precisely because their use is exploding. For the federal framework, see the FMCSA hazardous materials regulations. For the test, the key facts are the Class 9 assignment, the UN numbers, the special mark, and the extra care for damaged batteries.
Frequently asked questions
Why are lithium batteries regulated for transport?
Because they can undergo thermal runaway, a self-feeding overheating that causes fire. Damaged, defective, or poorly packed batteries are the biggest risk, so packaging, marking, and shipping are controlled.
What hazard class are lithium batteries?
They are generally Class 9 miscellaneous, because their fire risk does not fit classes 1 through 8. They carry specific UN numbers and a dedicated lithium battery mark.
What are the UN numbers for lithium batteries?
UN3480 for lithium ion shipped alone, UN3481 for lithium ion with or in equipment, UN3090 for lithium metal shipped alone, and UN3091 for lithium metal with or in equipment.
What is the best way to study lithium battery rules?
Learn the Class 9 assignment, the UN numbers, the special mark, and the damaged-battery rules, and keep your placard and marking recognition sharp with an app such as CDL Placards. Your state CDL manual is the authority.
