PHMSA letter of interpretation

Test T.7 Overcharge Procedures

Pipeline and Hazardous Materials Safety Administration · Oct 25, 2006 · Reference No. 06-0141

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.

Reggie’s quick take

Someone asked whether their Test T.7 overcharge procedures for lithium-ion batteries were correct under the UN Manual of Tests and Criteria, as referenced in the Hazardous Materials Regulations. The batteries have a 650 mAh nominal capacity and a 4.2 V maximum charge voltage. The agency said the 1.3 A charge current is correct, since § 38.3.4.7.2 sets the current at twice the manufacturer's recommended maximum continuous current. The agency also said the test voltage cannot be picked freely between 8.4 V and 22 V. Still, testing at a higher voltage than required will not invalidate the test.

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 requesting clarification of the requirements for Test T.7 overcharge procedures and conditions applicable to lithium-ion batteries in accordance with 38.3.4.7.2 of the UN Manual of Tests and Criteria, which is referenced in the Hazardous Materials Regulations (HMR; CFR parts 171-180). Specifically, you ask whether your procedures are correct in accordance with Test T.7 of the UN Manual of Tests Criteria.

According to your letter, your lithium-ion battery has a nominal capacity of 650 mAh (1C) and a maximum voltage charge of 4.2 V. During testing of your lithium-ion batteries, they are charged continuously at 1.3 A for a period of 24 hours with a select voltage range between 8.4 and 22 volts.

Section 38.3.4.7.2 reads: "The charge current shall be twice the manufacturer's recommended maximum continuous current." 'Therefore, your choice of 1,300 milliamp-hours (1.3 amp-hours) for the maximum charge current of the T.7 Test is correct.

Section 38.3.4.7.2 continues: "The minimum voltage of the test shall be as follows: a) when the manufacturer's recommended charge voltage is not more than 18V, the minimum voltage of the test shall be the lesser of two times the maximum charge voltage of the battery or 22V." It is your understanding, based on 38.3.4.7.2, that you may use an arbitrary number between 8.4V and 22V with which to conduct the T.7 Test the batteries described above. The language of Section 38.3.4.7.2 would not appear to allow the person testing a battery an arbitrary choice between the two voltages (8.4V and 22V). However, it is our conclusion that testing the battery at a higher voltage than is actually required will not invalidate the test.

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.