Grade B Cells

[Braddudya]

In real world terms can any explain what a "grade b" cell means? I understand that these cells are not a good choice if you are going to try to push their amp draw limit but for mild, let's say 1/2C use, what will be lost with grade B cells?

Half the cycle life?
More heat?

I guess I am just trying to make an educated decision about cost saving versus performance.

Thanks!

 

[Wattman]

A good question and more than a few go there and even build batteries from old laptops. Yes the things you mentioned but to me, the biggest problem is, lower quality cells means capacity difference among cells which translates to a battery going out of balance faster, in particular if you don't top balance the battery with a BMS...how most work...in an effort to prolong cell life. Charging cells to maximum voltage may help balance a less than uniform capacity battery but in doing so shortens the life of the battery.
Another way of looking at this philosophically which we learn in other life endeavor's is, there is no free lunch. Some would consider B grade cells a false economy. What is the cost you may wonder for lower cost cells even failing a bit faster? Your time. The hassle of dismantling the battery and fixing it when it falls out balance or building a replacement battery sooner and hassle of a BMS shutting off during a ride due to an out of balance parallel group within the battery.
Perhaps the most critical factor and most unknowable factor if buying a battery and not building it is....how good are the cells and how equivalent are they in capacity? When buying a battery there is a leap of faith and for some purists this is a bridge too far and why a small subset of the ebike community build their owner batteries and even fix them when they fail or start to wear out due to not having the best cells to begin with.
My thoughts.
In life, there is diminishing return with all things. If building a fresh battery some will capacity test every battery and then isolate them for decay for a period of a month or two. Others will pull them out of the box, randomly pick 10, load test them and if close enough for horseshoes build the battery. Labor and time has a cost and many don't believe its even worth it to build or even repair an aging battery. Some however do it for intellectual curosity. People that come to this site are generally interested in technology and want to learn about how things work. Honestly, I am slightly conflicted about the effort involved as well, but personally I would never build a battery with B level cells for reasons mentioned. Not just performance, but staying on the road and not always working on batteries that are more prone to failure due to lower quality cells. But if you like to spend more time building and fixing batteries, you can build a cheaper battery out of B level cells, no question and industry is flooded with them as well as too many unsuspecting ebike enthusiasts find out the hard way.

 

[Braddudya]

A good question and more than a few go there and even build batteries from old laptops. Yes the things you mentioned but to me, the biggest problem is, lower quality cells means capacity difference among cells which translates to a battery going out of balance faster, in particular if you don't top balance the battery with a BMS...how most work...in an effort to prolong cell life. Charging cells to maximum voltage may help balance a less than uniform capacity battery but in doing so shortens the life of the battery.
Another way of looking at this philosophically which we learn in other life endeavor's is, there is no free lunch. Some would consider B grade cells a false economy. What is the cost you may wonder for lower cost cells even failing a bit faster? Your time. The hassle of dismantling the battery and fixing it when it falls out balance or building a replacement battery sooner and hassle of a BMS shutting off during a ride due to an out of balance parallel group within the battery.
Perhaps the most critical factor and most unknowable factor if buying a battery and not building it is....how good are the cells and how equivalent are they in capacity? When buying a battery there is a leap of faith and for some purists this is a bridge too far and why a small subset of the ebike community build their owner batteries and even fix them when they fail or start to wear out due to not having the best cells to begin with.
My thoughts.
In life, there is diminishing return with all things. If building a fresh battery some will capacity test every battery and then isolate them for decay for a period of a month or two. Others will pull them out of the box, randomly pick 10, load test them and if close enough for horseshoes build the battery. Labor and time has a cost and many don't believe its even worth it to build or even repair and aging battery. Honestly, I am slightly conflicted about it as well, but personally I would never build a battery with B level cells for reasons mentioned. Not just performance, but staying on the road and not always working on batteries that are more prone to failure due to lower quality cells.

Thank you for the feedback. That is more or less what I believed. The point about balance is interesting and something I did not consider but I do plan to use a BMS.

For some more specificity I am talking about some big prismatic cells and they will be a 24s1p config. The savings look to be something like 25-30% which is really significant at this scale. If they last 1000 cycles that will outlast my personal use of the vehicle. Hopefully I will get some more opinions but at the moment I am still leaning toward the grade b cells.

 

[amberwolf]

Youd' need to find out what the specific seller means by grade b. Are they using the manufacturer grades? Or a system of their own? Or just calling something that isn't perfect this? Or?

If they are using hte manufacturer grades, then the manufacturer has specifications that determine what cells fit in each grade, which you can get from them.

If it's anything else, the seller would need to provide you with the specifications they use for their grades.

My guess is the seller is using it as a general term for all the rejects from QC (that probably should've been recycled).

 

[Braddudya]

Youd' need to find out what the specific seller means by grade b. Are they using the manufacturer grades? Or a system of their own? Or just calling something that isn't perfect this? Or?

If they are using hte manufacturer grades, then the manufacturer has specifications that determine what cells fit in each grade, which you can get from them.

If it's anything else, the seller would need to provide you with the specifications they use for their grades.

My guess is the seller is using it as a general term for all the rejects from QC (that probably should've been recycled).

After your comment I reached out to the seller to ask for more specifics and they told me that they are manufacturer rated and that they don't have specific specs for what classified them as grade B! That's scary. He also recommended the class A batteries instead. So I will probably go with the class A batteries for the higher price. But once cry once I guess!

 

[amberwolf]

If they are rated by the manufacturer, then you can check with the cell manufacturer for their specs on that specific model and version of cell.

If the manufacturer does not have published specs, I would not buy those cells, as you can't know what they are actually capable of, regardless of cell ratings.

Also, the seller might just have a crapload of junk cells and calll them different grades so they can charge more for the "higher grade" versions. Probably not, but it isn't unknown. Also not unknown for sellers to sell junk re-wrapped as a better brand / model of cell.

If you post a link to the seller's sale page for those cells, we may have advice to offer based on the actual posted information they have (and whatever we might know about the seller).

 

[batteryGOLD]

the # grade could depend on internal impedance increase over time/use..
example a 30mohm cell after many cycles goes 40-50mOhm , and lost 50% capacity?..
maybe it could be reused for new application with half or less consumption of original application designed?..

example #1: a scooter battery(30A peaks used) at 50% state of health could power a new veicule/application that only demands 15A or less of peaks, and battery keep alive instead of generating more pollution/trash.. remember to reconvert battery array.. or just send battery to trash can and build new one with new cells!! it's your choice.

example #2: imagine you reuse 100cells, you check datasheet reference and it says it is 20mOhm cell new. and you measure reused cell and is also 20mOhm, soo means this reused battery cells have just few cycles. so almost new.. maybe grade A- (dont know letters grade in EU, but I think A++ is the top..), any way careful because some cells keeps original internal impedance, but decreased capacity.. soo maybe you need to test all ,one by one. and it takes lot of time consuming..

example #3: imagine you recycle a cell original 30mohm and U measure it at 40-50mohm, soo maybe more than 500cycles, and half capacity output..
soo should we consider it a Z grade cell? the last letter of alphabet? is there a Z minus minus? one time I've tested a 20Ah battery and it only outuput 0,68Ah.. soo it means at 3,4% state of health..

Careful when buying cells from alixpres, bcausee most sellers sell used brand cells adv as new ones ,whit great advertise. only trust 1% of tha cn sellers or only if U are a friend of some one.. an also some cells have fake brand wraps.. and also some 18650 w half size cell inside & filled w sand!! what's happening with these people/sellers?!!

Anyone correct me if I'm wrong

 

[amberwolf]

(dont know letters grade in EU, but I think A++ is the top..)

Grading of cells and the designations used are not region-specific, etc., they are determined by the manufacturer (or whoever is doing the grading, or whoever is making up the advertising copy out of thin air ).

If there is legislation in some region requiring specific designations and grading methods / specifications, I'd be interested in seeing it, and how they enforce it on manufacturers and sellers not residing / manufacturing in that region.

 

[DogDipstick]

I believe it is a lottery, like a computer chip manufacture. There is a set of standards for "A" vs " B" and those cells that do not meet standard "A" will be sold as standard " B"... Like the computer chip " lottery" you get graded based on performance.

A good chip sells with high performance numbers, but some chips do neot meet this spec, and are sold under a lesser spec. It is the lottery of the production machine that determines this number.

 

[amberwolf]

Well, yes, AFAIK that's how most (all?) manufacturing processes work. But the actual cutoff points for each grade (for those items that are sold with various grades of quality) are determined (for many things) by the individual manufacturer. In this case, for cells, it's a manufacturer-specific thing (sellers, too, especially those that just buy lots of random assorted cells and rewrap them; they *may* also sort them by grade, or at least claim to).

There have been some things where a process is so well-known and identical in every manufacturer that grading is a part of the process itself and standards exist, or places like NIST have set arbitrary standards that manufacturers use either because they are required to or because it makes advertising their goods easier, for making sales vs some other company. I'm sure you deal with some of that in your work.

 

[999zip999]

It basically means not A grade not up to specs. If you're doing all the work of building a pack why Gamble with your time.