The one number on a robot battery pack datasheet that changes its DOT shipping section

To classify a robot battery pack for DOT shipping, calculate its total watt-hours by multiplying the pack's nominal voltage by its rated capacity in amp-hours. A pack above 100 Wh is Section IA, and so is any pack built from cells above 20 Wh. At or below those cell and pack thresholds, the pack can ship under the Section II exception if the package and carrier conditions fit; if they do not, it moves to Section IB as a fully regulated small battery. That one calculated number, not the cell rating in the marketing table, decides the packaging, the label, and the UN 38.3 evidence the shipment must carry.

I am at the receiving dock with a 48 V, 30 Ah AMR pack on the scale. You are on the other side of the table with the packing list in your hand. The scale beeps and settles. A forklift backs up outside and the alarm bleeds through the roll-up door. The datasheet is folded back to the spec table. You can see the lines the supplier wants you to see: Nominal Voltage 48 V, Rated Capacity 30 Ah, Chemistry Lithium-ion. The Energy line is blank. The carrier clerk has a label printer humming and a clipboard with a UN number field. He asks for the watt-hour. I do not answer from the sticker. I pull the calculator out of my vest pocket and put 48 times 30 into it. It reads 1,440. I circle it with a Sharpie. The pack is 1,440 Wh, so IA. The cells inside could be about 12.6 Wh each, and it would not matter for the pack total. That is the number that decides whether this is a Class 9 package or a lithium battery mark package.

The number I calculate before I read the rest of the datasheet

I do not trust the word energy on a datasheet. I trust the two lines that let me calculate it. Nominal voltage times rated capacity in amp-hours. If the capacity is in mAh, I divide by 1,000 first. If the datasheet gives cell capacity and a series-parallel configuration, I multiply out the pack. If it gives only watt-hours, I check whether that is pack watt-hours or cell watt-hours. The difference is not academic; it is the difference between a mark-only package and a fully regulated Class 9 shipment.

The threshold is unforgiving. A 24 V, 4 Ah pack is 96 Wh. A 24 V, 4.2 Ah pack is 100.8 Wh. One sits on the small side of the line. One is Section IA. That 0.2 Ah is not a rounding error at the dock.

I also use nominal voltage, not the charging voltage. A 48 V, 2 Ah pack is 96 Wh at nominal. If I use the 54.6 V charge voltage, I get 109.2 Wh. One number puts me in the excepted lane; the other puts me in a fully regulated lane. The datasheet may list both. I use nominal for the classification calculation.

The other trap is rated versus typical capacity. I use rated capacity for the shipping number. If the datasheet prints 99 Wh typical and 102 Wh rated, the pack is over 100 Wh. I do not get to choose the friendlier number. The shipping section is a regulatory line, not a performance estimate.

Why the pack's watt-hours, not the cell's, set the lane

The pack's total watt-hour rating, not the individual cell rating, is the number that determines its shipping section. That is the first check. Most robot packs are series-parallel assemblies of small cells, and the pack total crosses 100 Wh faster than people expect. A 10S4P pack of 3.6 V, 3.5 Ah cells is 504 Wh. Each cell is about 12.6 Wh. The cell number is not the shipping number. The pack is 504 Wh, so it is Section IA.

The cell rating still matters at the edge. If a cell itself is over 20 Wh, the pack is Section IA even if the pack total is under 100 Wh. A 3.2 V, 100 Ah cell is 320 Wh. A two-cell pack is 640 Wh. Even a single cell over 20 Wh is enough to push the pack into IA. For most small-cell robot packs, the 100 Wh pack threshold is the one that bites. For large-format packs, the 20 Wh cell threshold can decide it before you ever get to the pack total.

This is why I ask for both numbers on the datasheet: pack watt-hours and cell watt-hours. I want the supplier to show the calculation, not just print a section. If the supplier cannot show the calculation, I do not accept the section on the quote as a classification.

What changes at 100 Wh: packaging, labels, paperwork

The U.S. ground rules sit in 49 CFR 173.185. The IA, IB, and II language comes from the packing instructions that carriers and inspectors use. I treat the section as the operating label for the same thresholds.

IA is the full package. The pack ships as UN 3480, lithium ion batteries, Class 9. You need UN specification packaging, the Class 9 hazard label, the UN number and proper shipping name, a shipper's declaration, and the UN 38.3 test summary for the pack. For air, you also have the Cargo Aircraft Only question and the operator variations. I keep the box's closure instructions with the shipment because a UN mark without the right closure is just a box with a mark on it.

IB is not IA lite at the dock. It is still fully regulated. The cells and batteries are at or below 20 Wh and 100 Wh, but you are not using the Section II exception. The package carries the Class 9 label, the lithium battery mark, and the shipper's declaration. The packaging follows the IB column, with a strong outer package and the right closure, not the Section II exception. Do not assume the box you used for Section II will carry over.

II is the excepted lane. The package gets the lithium battery mark, not the Class 9 label. You still need a strong outer package, the package net quantity limits, and the UN 38.3 test summary. The paperwork is lighter, but it is not absent. Excepted does not mean unregulated, and it does not mean untested.

The easy visual check is this: IA and IB get the Class 9 label; II gets the lithium battery mark. If I see a Class 9 label on a small pack, someone either chose IB on purpose or misclassified. If I see only a lithium battery mark on a 1,440 Wh pack, the shipment stops.

The IB versus II decision nobody explains well

The table looks like three rungs. It is not. It is two lanes: fully regulated, which is IA and IB, and excepted, which is II. The watt-hour thresholds tell you whether the battery is big or small. They do not tell you whether you are allowed to use the exception. That depends on the package net quantity, the carrier's acceptance rules, and whether you can meet the Section II conditions.

If the pack is at or below 100 Wh and the cells are at or below 20 Wh, you are in the small class. You can use Section II if the package fits the exception and your carrier accepts it. If the package is over the Section II limit, or the carrier will not take the exception, you do not jump to IA. You move to IB. That is the reason IB exists. I have had a small pack that was Section II on paper but IB in practice because we were putting several packs in one box and the net quantity pushed us out of the exception. The pack did not get bigger. The shipment did.

IB still requires UN 38.3. So does II. The difference is not testing; it is the regulatory lane. A supplier who says the pack is IB because it needs UN 38.3 testing is not giving you a classification. They are giving you a fragment of one.

What I put in the RFQ and what I check at the dock

I put four lines in the RFQ. Pack watt-hours, calculated as nominal voltage times rated capacity in amp-hours. Cell watt-hours. The intended shipping section and packing instruction. The UN 38.3 test summary with the pack part number on it. I also ask for the label artwork. If the supplier can print the watt-hours on the pack label, I want that. If they cannot, I calculate it and put it on our internal travel sheet.

At the dock, I check the label against the datasheet. If the label says 48 V, 30 Ah, but no watt-hours, I add the calculation. If the label says 1,440 Wh and the datasheet says 1,200 Wh, I stop and find out which one is the pack. I check the UN 38.3 summary's pack part number against the label. I check the shipping section on the shipper's declaration. If the package is Section II, I check the net quantity.

The UN 38.3 summary is not the same as a cell datasheet. A custom pack is a battery, not a box of tested cells. The summary should cover the pack model and list the tests, T1 through T8, with results. If the pack is a new configuration, the summary needs to cover that configuration. I have seen suppliers send a cell-level summary and call it a pack summary. That is not the document the carrier is asking for.

For IA, I also keep the UN specification packaging test report and the closure instructions in the shipping binder. The box has a UN mark. The mark is not a suggestion. The closure instructions are part of the package.

Where this goes wrong in the real world

The most common error is treating 100 Wh as a round number. It is a line. A pack at 100.8 Wh is over the line. A pack at 99.9 Wh is under it. The datasheet's typical capacity may put you on one side; the rated capacity may put you on the other. I use rated.

The second error is using the cell watt-hours as the pack watt-hours. A small cell does not make a small pack. A 504 Wh pack is IA even if every cell inside is under 20 Wh. The pack total is the first number.

The third error is assuming Section II means no testing. Section II is an exception from some packaging and marking requirements. It is not an exception from UN 38.3. The test summary still has to exist and still has to match the pack.

The fourth error is treating IB as a paperwork choice. IB is a fully regulated shipment. It carries the Class 9 label and the shipper's declaration. If you choose IB, you are choosing the fully regulated lane for a small battery. You are not choosing a lighter version of IA.

PHMSA enforces the hazardous materials rules in the United States, and misclassification can carry civil penalties. I do not use that as a scare line. I use it as a reason to put the calculation on the shipping paper and to keep the UN 38.3 summary with the shipment. The penalty is not the only cost. A pulled package sits, the RMA misses its slot, and the customer who was waiting on the robot gets a new date.

The number on the datasheet is not a formality. It is the first decision in the shipment. If the watt-hours are wrong, the section is wrong, the label is wrong, the box is wrong, and the paperwork is wrong. I calculate it every time, even when the supplier has already printed a section on the quote.