The United States Pipeline and Hazardous Materials Safety Administration (“PHMSA”) transmitted a February 5th interpretive letter addressing the application of the federal Hazardous Materials Regulations (“HMR”) to lithium ion batteries.
PHMSA is responding to a July 22, 2025, query from Currie Associates, Inc. (“CAI”).
CAI requested clarification of the HMR applicable to size limits for lithium ion batteries with respect to exceptions for smaller cells or batteries and clarification provided in a previous letter of interpretation (See Reference No. 15-0009).
CAI indicated that the definitions section in 38.3.2.3 of the Eighth Revised Edition of the United Nations (UN) Manual of Tests and Criteria (MTC) now defines a battery as:
… “two or more cells or batteries which are electrically connected together and fitted with devices necessary for use...”
CAI seeks confirmation that:
- A lithium ion battery consisting of two cells, each exceeding 20 watt-hours (Wh) but with a combined total of less than 100 Wh, qualifies for the exception outlined in § 173.185(c)(1)(i); and
- The prior clarification remains valid.
PHMSA responds in the affirmative, stating that the letter of interpretation (Ref. No. 15- 0009) cited remains valid. Further, it confirms that:
… the 100 Wh limit applies to the assembled battery, and that the 20 Wh limit for individual cells does not need to be considered for the component cells within that battery.
The February 5th interpretive letter also states that while the UN MTC has updated the definition of a “battery,” this revised definition does not invalidate the 2015 letter of interpretation. If the assembled battery’s total energy density is under 100 Wh, the exceptions specified in § 173.185(c)(1)(i) apply, even if each component cell exceeds the 20 Wh limit.
A copy of the interpretive letter can be found here.
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