(you know who you are
)
"what is nominal and what is capacity?" when it comes to the batteries we're buying, and advertisers/sellers use both to describe one thing: capacity, which leaves us buyers in that same dilemma.
This statement makes me feel like you still don't grasp the meaning and significance of the word nominal.
But one place we can agree is how atrociously the resellers advertise their products on aliB and aliX. It is not uncommon to see a product listing that states something like: GRADE A 2020 NEW 2019 285Ah 280Ah 272Ah LIFEPO4 LITHIUM PRISMATIC SOLAR BATTERY CELLS 3.2V 12V HOME ENERGY STORAGE FORKLIFT (or product listings that list one thing in the title and 2 or 3 conflicting things in the description--this is especially common with BMS listings, where many things get copy pasted without review).
Generally speaking one of the first things I do when I am interested in cells on either site is contact the seller and ask for the actual cell datasheet. About 3/4 of the time they can provide an actual datasheet. If not, I usually move on. The datasheets come from the manufacturer and are free of the hyperbole and misrepresentation of the reseller. However, a datasheet is a reference point of what a good new grade A cell is, not a guarantee that the specific grey market cells you are looking at (which are often grade B cells, old stock, etc) will meet every specification, if it is represented as Grade A, it should. This is where asking for assurances (and verification where possible) from the reseller comes in. If you ask them clear short direct questions, they will sometimes give you an honest answer, and sometimes they will sidestep or be vague (either because they don't know or they know the answer is not what you want to here). Generally speaking, my baseline assumptions are: the reseller (1) has partial and limited information (2) won't always accurately or fully relay the information they do have.
This situation is where I think the term "nominal capacity" has no value and is actually misleading in this context.I'm simply reiterating that until the baseline of what the actual battery capacity rating is is agreed upon, we'll continue wondering if we're getting what we've paid for.
If you want clarity just look to the datasheets. While I think the broad problem you are sensing (misleading and confusing advertising by resellers) I think a big part of what you are struggling with comes from a misunderstanding and confusion over unfamiliar terms. Ignoring resellers for now, datasheets come from the manufacturer, and datasheets define
minimum capacity. There is no grey area there. That is the capacity that a cell must meet to pass QA and be considered grade A. In my opinion people (and resellers) overcomplicate this.
For a 280Ah EVE cell, the minimum capacity a grade A cell should have is 280Ah. Full stop.
For a 100Ah FREY cell, the minimum capacity a grade A cell should have is 100Ah. Full stop.
For a 100Ah CALB cell, the minimum capacity a grade A cell should have is 100Ah. Full stop.
^ In all three of the above examples the minimum capacity and the nominal capacity are the same. In fact I believe this is the case for every cell datasheet I have seen.
Actual capacity is different, the manufacturing process is not 100% precise, so actual capacities may vary somewhat, and manufacturers may target a capacity above the minimum capacity for other reasons.
CALB is one of the examples of a company doing it best in my opinion.
Nominal Capacity = Minimum Capacity (i.e. The CALB CA180 (nominal capacity of 180Ah must be at a
minimum, 180Ah)
Actual capacity is tested during QA and handwritten on the cell down to the tenth of an Amp hour, and included in a cell report for each cell.
Actual capacity exceeds nominal capacity (minimum) capacity by a good margin. 10% over minimum capacity in the examples I have seen.
