First I am certainly not an expert on this and my knowledge is quite limited. If you think I am misunderstanding something please bring it up, or if you are a reseller and have some wisdom to share on the subject please do.
I keep reading on this thread opinions as to whether these are A cells or B cells. Is there a standard for A and B cells, or is this a subjective evaluation. Do B cells last as long as A cells?
There is not a single standard, but it is also not a subjective evaluation. A grade and B grade cells refer to whether a cell meets the manufacturer specifications. B grade cells are cells that are out of spec in one or more areas (not all of these areas are a big deal for our relaxed application--for instance a 150Ah cell having a capacity of 147AH would not be a dealbreaker for me so long as they are matched).
Just as important (probably more important) as knowing if cells are grade B or not, is knowing why they are grade B, we don't need absolute precise perfection for our application and shouldn't count on it at the price point people are expecting to pay. Due to this and because so many resellers either misrepresent or are ignorant of the cell grade, don't get too hung up on this factor alone.
Subjective and marketing BS. No standard, and sellers will say whatever they think will make you buy them.
I give it no weight and only go by what other people say who have already bought cells from them.
I doubt this is a real designation. No one has a specification for what those letters mean. There's no standard.
I think you guys may not be 100% clear on the terms, and are misplacing your skepticism. I fully share your frustration and skepticism towards what the
resellers classify as grade A or grade B. I do not trust resellers to be honest about cell grade, this is just the unfortunate reality of things.
But I think you are missing the point if you think cell grade is meaningless or just marketing BS. I believe these conclusions are based on a misunderstanding of what cell grades are supposed to mean.
As I understand it, battery cell grades are not universal industry wide standards (which seems to be what you are thinking
@nebster), but I don't think its marketing BS as you are thinking
@sremick. Cell grading/sorting is specific to each manufacturers specifications and QA process. Grade A cells meet all the manufacturers specifications, Grade B cells are out of spec or failed QA in one or more areas but (in theory) are still usable/suitable for sale, Grade C cells are not suitable for use/sale and should be destroyed/recycled but some manufacturers apparently don't use the Grade C designation and unfortunately include these with Grade B.
Basically A, B, C grade are shorthand for (A) meets or exceeds specs (B) does not meet specs in one or more areas but is still usable (C) unusable. Cell grade is always relative to the manufacturer specifications, not universal across manufacturers.
Further complicating things, there are at least a half dozen reasons cells can be demoted to grade B, some of these are troubling, while many are not a huge concern for our application. Resellers buy cells from manufacturers or middlemen in big batches and from what I understand rarely know the reason the cells they are buying did not make the cut. Testing and matching before sale can help mitigate some of the uncertainty, but it is my impression that most resellers only do basic testing.
These are two of the best and most straightforward videos I've found on the subject. They cover:
- What are grade A, grade B, and grade C cells
- How lifepo4 batteries are produced and where in the process B and C grade cells come from
- The reasons a cell can be derated to grade B
- How to (somewhat reliably) distinguish grade A and grade B cells
- Some of the ways manufacturers test cells, and some of the ways you can test cells
What are grade A and grade B cells
How to distinguish grade A and grade B cells