PHMSA letter of interpretation

Design-type testing of lithium-ion cells and batteries

Pipeline and Hazardous Materials Safety Administration · Jul 27, 2007 · Reference No. 07-0106

PHMSA says to use caution with this letter. On August 6th, 2014, PHMSA published Final Rule, HM-224F, which amends the regulations for lithium batteries. The rule harmonizes the HMR with many of the provisions in the UN Model Regulations, ICAO Technical Instructions, and IMDG Code. Additionally, the exceptions for small and medium lithium batteries formerly found in special provisions 188 and 189, have been moved to § 173.185(c). Please refer to the most recent version of § 173.185 for information on shipping lithium batteries. The most current version of the regulations can be found in the eCFR at www.ecfr.gov.

Interprets: 49 CFR § 173.185

Reggie’s quick take

A company asked whether its hybrid electric vehicle battery, built from 192 A123 lithium-ion cells wired together through a circuit board, could count as a "battery assembly" and skip design-type testing under section 38.3 of the UN Manual of Tests and Criteria. PHMSA said no. Each cell passing its own tests does not exempt the full battery, and a circuit board that can be disconnected does not make the cells a battery assembly. Under § 173.185, a new battery design type generally needs the section 38.3 tests, even when its cells have already passed. The company could instead seek a special permit if it believes its design is equally safe.

Written by AI (Claude) on Oct 22, 2026. Robots make mistakes and leave things out, so the letter below is what counts. Not legal advice.

This is in response to your letter dated May 23, 2007 requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to design- type testing of lithium-ion cells and batteries. The specific requirements you address are contained in section 383 of the United Nations Manual of Tests and Criteria and are implemented through the provisions of § 173.185 of the HMR.

In your letter you describe a hybrid electric vehicle battery system consisting of 192-3.3 volt A123 cylindrical lithium-ion cells utilizing approximately 518 grams of aggregate equivalent lithium content. The battery system is equipped with a system that monitors cell voltage and temperature and incorporates a service disconnect feature. Each cell passed the design-type tests in section 38.3 of the UN Manual of Tests and Criteria and the cells in this assembly are electrically connected by a circuit board. It is your opinion that since the individual cells passed the applicable tests and incorporate additional safety systems, the cell assembly constitutes a "battery assembly" as described in 38.3.3 of the UN Manual of Tests and Criteria and thus the assembly is not required to be tested in accordance with the design-type tests outlined in section 38.3.

We do not agree. The system you described meets the definition of a battery or a battery pack, defined in section 38.3 of the UN Manual of Tests and Criteria as one or more cells electrically connected together by permanent means, including case, terminals and markings. Except for single cell batteries, each new lithium cell and battery design-type is subject to the tests in the UN Manual of Tests and Criteria, even if the cells that make up the battery have been tested. The fact that the cells are electrically connected by a circuit board that can be disconnected does not mean this assembly of cells constitutes a battery assembly.

If you believe your hybrid electric vehicle battery system provides and equivalent level of safety to the HMR requirements without additional testing, you may wish to apply for a special permit through the Office of Hazardous Materials Special Permits and Approvals at 202-366-4535.

A letter of interpretation applies the regulations to the facts the requester described. It isn’t a regulation and isn’t legal advice. The agency’s copy.