PHMSA Set a Weight Limit on Lithium Batteries. It Never Defined What Skips It.

On August 4, 2026, PHMSA published a final rule that lets companies carry far more lithium batteries as tools of the trade before the full Hazardous Materials Regulations apply. Docket PHMSA-2025-0091, known as HM-268C, takes effect September 3, 2026. It replaces the old blanket 200 kg (440 lb) weight cap on all Materials of Trade combined with a battery-specific structure: 30 kg per cell or battery, 500 kg aggregate per vehicle. Standalone spare batteries - the ones a contractor tosses in a truck bed - get that new, higher number.

Batteries "contained in equipment" get something different: no weight limit at all. The rule sets that carve-out in its own operative text and never says what "equipment" means for the purpose of using it. Thirteen parties commented on the proposal. The one safety-focused objection in the record argued about the standalone-battery figure. Nothing in that objection, and nothing in PHMSA's response to it, touches the exemption that actually has no number attached.

The Rule PHMSA Actually Wrote

New 49 CFR 173.6(a)(7)(iii) states that, "[e]xcept when the cell or battery is contained in equipment," lithium cells and batteries carried under the Materials of Trade provision "may not exceed 30 kg (66 pounds) net weight for each cell or battery and 500 kg (1102 pounds) aggregate net weight on a motor vehicle." The same paragraph requires every battery covered by the provision - standalone or installed - to meet the testing criteria in Part III, sub-section 38.3 of the UN Manual of Tests and Criteria. That requirement doesn't loosen for the equipment carve-out; the weight limit does.

A companion change to 173.6(d) confirms the split is deliberate, not an oversight: the general 200 kg aggregate cap that applies to all other Materials of Trade on a vehicle is explicitly waived for batteries authorized under the new provision. PHMSA frames this as a narrow fix for a specific set of workers - the rule states its allowance applies to companies in "construction, landscaping, mowing, tree service, food service, and entertainment," and PHMSA estimates the change will produce $14.4 million in annualized cost savings (2024 dollars). Nothing about the scale of the intended beneficiaries reads as reckless. The rule reads like a sensible fix for a specific, narrow annoyance: a landscaping crew's cordless mowers and trimmers, batteries and all, shouldn't trip a 440-pound ceiling meant for loose hazmat.

What "Equipment" Doesn't Mean

A full-text search of the final rule for "equipment" turns up the phrase repeatedly - in the operative regulatory text, in PHMSA's cost-benefit discussion, in its description of who benefits. Nowhere does the rule define it, or set any boundary on it: no size limit, no category list, no requirement that the equipment itself be inspected or registered. The same search turns up nothing at all for "recall," "counterfeit," "enforcement," "penalty," or "inspection." None of that is unusual for a rule of this type - Materials of Trade exceptions have always run on trust and ordinary practice rather than itemized enforcement machinery. What's unusual is the asymmetry: everywhere else in this same paragraph, PHMSA writes in exact numbers. Thirty kilograms. Five hundred kilograms. Two hundred kilograms it's waiving. Then, for the one category it just uncapped, it writes a word with no attached definition.

To be clear about what this is and isn't: no instrument says PHMSA intends "equipment" to be read broadly, and nothing found this Run suggests anyone is treating the term that way in practice. This is a reading of what the rule's text does and doesn't say, not a forecast of misuse. A hazmat compliance specialist could reasonably argue that "equipment" already carries an ordinary, working meaning in HMR practice - a power tool a battery is installed in and powers, not a shipping container of loose cells relabeled for convenience - and that ordinary enforcement discretion, plus the general prohibition on misclassifying a shipment as a Material of Trade in the first place, would constrain obvious abuse even without a codified cap. That may well be true. It is also not written down anywhere in this rule.

The Objection That Missed the Bigger Change

Two of the thirteen commenters raised safety concerns. The Commercial Vehicle Safety Alliance argued that the existing 440-pound allowance was already sufficient and that "increasing the quantity of lithium batteries directly correlates to the severity of potential incidents," citing "recent crashes and fires involving lithium batteries that have resulted in significant highway and port closures." An individual commenter, William Forbes, called the increase "astronomical," argued it poses an "inherent risk" without adequate safety data, and said the change "would place an undue burden on first responders." PHMSA's response called the increase "a modest and incremental adjustment - not an 'astronomical' expansion" and concluded flatly that "these revisions will not have any adverse impact on safety."

Read that exchange closely and the shape of it stands out: every sentence on both sides is about the aggregate number - 200 kg going to 500 kg for standalone batteries. Neither CVSA's letter nor Forbes's comment, as reflected in the rule's own text, contains a sentence about batteries installed in equipment specifically. The exemption with no ceiling at all - the more open-ended of the rule's two changes - was never the subject of an objection, so PHMSA's response never had to address it either. That's this Article's own reading of the comment record, not a gap PHMSA or any commenter has acknowledged - nobody on either side of this exchange has said the equipment carve-out went unexamined; it's what's missing from the record, not a stated finding in it. It's also not a criticism of CVSA's judgment; a trade association responds to what a proposed rule visibly changes, and the headline change was the number. It does mean the part of the rule's own record built to pressure-test a safety tradeoff never touched the part of the rule that has no test built in.

What a Well-Run Operation Does Differently

An operator whose battery-powered fleet is large enough to lean on the equipment exemption - a construction firm running dozens of cordless tools, a landscaping company with a truck full of powered mowers - is relying on an undefined term with no enforcement history yet attached to it. The rule doesn't require documenting why a given battery counts as "contained in equipment" rather than a loose spare riding alongside it. Nothing in the text asks for that record. But a compliance function that waits for PHMSA to draw that line, rather than drawing a defensible one internally now, is choosing to find out where the boundary sits from an inspector rather than from its own paper trail. That's not a rule requirement described here - it's what the gap in this rule leaves an operator to decide for itself, and it's worth deciding on purpose rather than by default.

Source note: This Article is drawn from PHMSA's final rule, "Hazardous Materials: Reducing Burdens on Domestic Companies Using Battery-Powered Equipment in Trades" (Docket PHMSA-2025-0091, HM-268C), published in the Federal Register on August 4, 2026, and effective September 3, 2026.