Shipping products with Lithium (ion) batteries, who determines (Wh) capacity? - Page 1
Forum section: electronics / general

author: StefanHamminga
author_rank: Contributor
timestamp: November 01, 2023, 07:07:15 am
content: I hope someone here can help clarify something: When shipping a product with a built-in battery (and have an owner take it along on a flight), who determines the battery capacity for the 100Wh IATA limit? And how is it determined?Reading up on UN3481 and related norms I wasn't able to find anything on who and how the capacity is determined, just how to handle a product with a given capacity.One reasons to not just add-up the cell capacities is to compensate for under-performing cells (even the best of them rarely reach the 'rated' capacity) and pack construction, to offer the best actual battery life within the 100Wh limit. Another reason is to use a larger pack de-rated (the device would have a built-in charger to ensure this) to increase the lifespan of the battery.

author: mtwieg
author_rank: Frequent Contributor
timestamp: November 01, 2023, 01:26:56 pm
content: It's been a while since I looked at these issues, but I believe capacity is covered in UN 38.3 (I'm assuming your cells/batteries are already tested, or will need to be). Capacity is something you specify on the test specification, I don't believe any of the tests actually measure capacity (again, it's been a while).I recall that they really care about the amount of lithium in the battery, and capacity is a rough proxy for that. I don't believe the standards care about actual cell performance. As for de-rating a pack... AFAIK there's nothing in the written rules against this, but I have to assume it wouldn't get very far.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 01, 2023, 02:22:16 pm
content: Quote from: mtwieg on November 01, 2023, 01:26:56 pmProbably not, because li-ion cells do not have metallic lithium at all*, and any lithium is in inert form (lithium ions). Instead, what makes li-ion cells dangerous, thermal runaway is due to cathode reactions (e.g., cobalt oxides) and secondarily, flammable electrolyte. They care about the energy that can be released in an uncontrolled runaway reaction, and indeed there is good correlation between rated energy capacity and that.*) abused, old cells have a small-ish amount

author: tszaboo
author_rank: Super Contributor
timestamp: November 01, 2023, 04:27:29 pm
content: Whoever signed the DoC of the product.UN 38.3 is for bare batteries, you request a test report from the manufacturer if you need to ship that.

author: nctnico
author_rank: Super Contributor
timestamp: November 01, 2023, 04:40:56 pm
content: Quote from: tszaboo on November 01, 2023, 04:27:29 pmNo. UN 38.3 is also for battery packs (cells assembled in a housing and typically with a BMS).

author: tszaboo
author_rank: Super Contributor
timestamp: November 01, 2023, 05:12:41 pm
content: Quote from: nctnico on November 01, 2023, 04:40:56 pmIn English the term battery means cells, or battery created from multiple cells.

author: nctnico
author_rank: Super Contributor
timestamp: November 01, 2023, 05:19:45 pm
content: If you read the actual tests, it is very clear that UN38.3 applies to battery packs. I have been involved in getting battery packs through UN38.3 certification myself.

author: TimFox
author_rank: Super Contributor
timestamp: November 01, 2023, 05:20:59 pm
content: Quote from: tszaboo on November 01, 2023, 05:12:41 pmI totally agree with tszaboo about battery vs. cell, but using "battery" for a single cell is another example of careless modern usage eliminating the distinction between terms that are not synonymous, making it difficult to distinguish between two different objects. Perhaps we need to use "pile" to deal with those who use battery to mean cell. (A Voltaic pile is defined as a series connection of multiple Voltaic cells.)

author: Marco
author_rank: Super Contributor
timestamp: November 01, 2023, 05:21:41 pm
content: Quote from: tszaboo on November 01, 2023, 04:27:29 pmSo if a company designs its own battery pack they can self certify to whatever they find reasonable?If the cells add up significantly higher than 100Wh when fully charged, but the BMS limits it to 100Wh for the pack in most circumstances and they think that's fine ... that's fine?

author: nctnico
author_rank: Super Contributor
timestamp: November 01, 2023, 05:23:56 pm
content: Quote from: StefanHamminga on November 01, 2023, 07:07:15 amYou are trying to find loopholes which aren't there. Pack capacity is nominal capacity (as specified by the cell manufacturer) of all cells added up.And if you think about it, it is logical. It is all about the worst case amount of energy that is stored in a pack as that is a direct measure for the amount of damage a battery pack can do.

author: uer166
author_rank: Super Contributor
timestamp: November 01, 2023, 05:27:57 pm
content: Quote from: nctnico on November 01, 2023, 05:23:56 pmWhat's stopping you from asking the cell manufacturer to de-rate the cells on datasheet/spec? It's a paper change, so there's definitely room for a gray zone. The Tesla LV battery is rated 99Wh, which coincidentally is just below the air ship limit of 100Wh. Do you really think those cells where engineered to be exactly at 99Wh in total? There was for sure some specmanship there.

author: nctnico
author_rank: Super Contributor
timestamp: November 01, 2023, 05:55:56 pm
content: And involvement from the legal department to have plausible deniability.

author: tszaboo
author_rank: Super Contributor
timestamp: November 01, 2023, 07:24:27 pm
content: Quote from: nctnico on November 01, 2023, 05:19:45 pmDon't disagree about the claim about battery packs, and the applicability of UN38.3. What I'm saying is battery means 1 cell or 2 cells or however many cells and balancing circuit and whatever in English.

author: nctnico
author_rank: Super Contributor
timestamp: November 01, 2023, 08:03:17 pm
content: Quote from: tszaboo on November 01, 2023, 07:24:27 pmYou are right. Your term 'bare batteries' threw me way off.

author: jbb
author_rank: Super Contributor
timestamp: November 01, 2023, 08:08:51 pm
content: Quote from: uer166 on November 01, 2023, 05:27:57 pmWell, the product engineering team would have ordered a 99 Wh battery, and the battery design team would have calculated how much active ingredients to put into each cell on that basis. Pretty sure the formal Wh is calculated by rated nominal voltage (V) * rated capacity (mAh or Ah) * number of cells.For us mortals who don’t have a battery factory in our back pocket, I guess that it comes down to the spec sheet and markings applied by the manufacturer.I could be mis-remembering but I think there was also a limit of max 20 Wh per cell.I suspect a lot of laptop batteries are now designed on the same ‘just under 100 W’ basis.

author: artag
author_rank: Super Contributor
timestamp: November 01, 2023, 09:18:31 pm
content: I guess I'd have a problem if I took this on a flight then ?https://www.ebay.co.uk/itm/313032517825

author: nctnico
author_rank: Super Contributor
timestamp: November 01, 2023, 09:34:15 pm
content: Quote from: artag on November 01, 2023, 09:18:31 pmNo. The capacity is likely to be 0.5Ah so no problems there.

author: thm_w
author_rank: Super Contributor
timestamp: November 01, 2023, 10:04:07 pm
content: Quote from: jbb on November 01, 2023, 08:08:51 pmCorrect:https://www.fedex.com/content/dam/fedex/us-united-states/services/LithiumBattery_JobAid.pdfQuote from: Siwastaja on November 01, 2023, 02:22:16 pmFor li-ion yeah, though Fedex uses it as sort of a catch-all: if Wh is 100 to 300 OR lithium content 2 to 25g then you cannot transport via aircraft, goes ground:https://www.fedex.com/content/dam/fedex/us-united-states/services/Shipping-Lithium-Batteries-via-FedEx-Ground.pdfhttps://www.fedex.com/content/dam/fedex/us-united-states/logistics/Lithium-Battery-Shipping-Tool.pdf

author: Siwastaja
author_rank: Super Contributor
timestamp: November 02, 2023, 11:16:16 am
content: Quote from: uer166 on November 01, 2023, 05:27:57 pmAs usual, "cheating" "a bit" is unlikely to cause any problems - especially if there are no incidents - but get too greedy and game the system too much, and some day it hits you.There are well-established ways to define li-ion energy capacity and while you could "roll your own" which differs "from the usual" by say 5%, but try to do 50% and I'm sure someone, at some point, gets interested and will challenge your methodology.

author: StefanHamminga
author_rank: Contributor
timestamp: November 02, 2023, 07:02:38 pm
content: Quote from: mtwieg on November 01, 2023, 01:26:56 pmVery interesting, thank you! I read through it and while it doesn't explicitly go against de-rating it specifies "fully charged" as a test condition, mentioning 'design capacity', so indeed it would be hard to deviate far from the cell manufacturer's data without a good reason.The procedure to determine the rated capacity is defined in IEC 61960, chapter 7.3.1 (a 0.2C discharge of a full cell, in a nutshell).Quote from: tszaboo on November 01, 2023, 04:27:29 pmThe copy I have in front of me specifically mentions applying to 3481 (built-in battery packs).Quote from: Marco on November 01, 2023, 05:21:41 pmThere is a point explicitly mentioned that would definitely help do this: The manufacturer sets the end point (discharge) voltage. Even the IEC (above) test procedures use two different end voltages for determining capacity and life of their standard cells.