How to tell the difference between Grade A and Grade B cells.

ghostwriter66

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How to tell the difference between Grade A and Grade B cells. AND why you should always pay with CREDIT CARD.

Going to make this sort of in bullet form – otherwise this will go on for many of pages of rambling which this will probably be anyway..

Before I start …25C is 77F – the perfect temperature for LFP. Remember – LFP is a CHEMISTRY – strange things start happening as you get further away from 77F… Also keep in mind that honestly – no one really understands LFP. It’s a weird chemistry – it works remarkably well – but there is still allot of voo-doo in how it works. (Voo-doo being a technical word here – LOL)

But back to Battery ratings.

There are actually (5) five accepted commercial LFP ratings in China used by commercial companies.

GRADE A+
GRADE A-
GRADE B
GRADE C
SECOND-HAND


When dealing with the Anglos, the Chinese will often refer an A+ and A- as simply GRADE A and B/C as B.

I will not discuss Grade C or second hand – I am going to say that I have seen VERY little Grade C or Second Hand here on this forum. Both are obvious – leaking – dented (badly), warpage, and both will measure 3.2V but the moment u put a load on them they crash to below 1V instantly ...

And – although not a scientific observation, but as of 2021, you can typically tell your Grade B and below simply by their packaging. The ppl that are passing off Grade B for A’s and trying to separate you from your money most usually is not wanting to waste allot of the profit in doing professional secure packaging but instead just drop it in a cardboard box – add allot of tape – and hope you don’t open them until after the dispute phase is over.

NOW – this will probably be the most important thing to take away from this. There is absolutely NO standard between each company on how they rate batteries. We have purchased some critical 3.2V 280Ah LiFePO4 batteries used for medical stuff from company XYZ that was considered GRADE C by that company BUT turned out to be better than any GRADE A+ listed by any of the normal LFP Alibaba companies.

My ex-boyfriend has an Audi R8. He loved that car. If it was a battery he would give it a GRADE A+. I hated it – you literally had to fall into the car to get in. And you literally had to roll out to get out. I could barely see over the dashboard. And the seats were hard and uncomfortable. I would give it a B-.

So batteries, as in car ratings, is in the eye of the beholder, or manufacturer – so to speak.

That’s why DATASHEETS are VITAL. And not the datasheets the VENDOR supplies BUT the datasheet of the manufacturer. !!

(Beat a dead horse time) …BUT one of the things that kills me most is when ppl do NOT read the datasheet of the particular manufacturing company they are purchasing the batteries from. This is vital. You MUST have a datasheet to compare the results you are getting to what they said you should be getting.

The first thing I do is weigh each and every battery we receive. That right there tells me if its going to meet 90% of my expectations. Testing voltage rarely tells me anything. (Heck a dead 9V battery still reads 9V). The second thing I do is an IR test.

SO the best way to know if a cell is actually a Grade A all the way thru Second Hand is look at the manufacturers specifications and compare it to your results.

The (6) six key parameters that must be checked to determine the proper grading is:

Appearance, Size and Weight, Capacity, Internal Resistance, Self-Discharging Rate, and Capacity Recovery.


Every manufacturer will grade every battery coming off the line against these 6 parameters. Most manufacturing companies have this done by computers and an automated process. But any of these 6 factors can cause an GRADE A to go to C in a heartbeat. The issue for US is that these reputable companies will sell their GRADE C’s to a distributor as a GRADE C for pennies on the dollar, and the distributor turns around and sells the Grade C to someone as a GRADE A and hope you don’t test IR or Capacity Recovery or something before its too late to dispute. ALIBABA is VERY much against companies doing this and will support you in getting your money back for this.

APPEARANCE: Each battery is produced with a QR code that allows the end-user (YOU) to get information about the battery and get assistance for warranty and customer service. …. In China, Grade B cells do NOT have a warranty, so 100% of the manufacturers will scrape off the QR code before pushing them to a reseller as B-Grade. Sometimes the manufacturer will not scrape the QR code but simply put a new black insulating panel over it. Either way – missing, scratched, or covered with a black strip -- its a GRADE B cell (normally). If there is a QR code under the strip of black plastic – IT’S A GRADE B….

SIZE AND WEIGHT: So this one is a little tricky. Batteries will be different size and weights at different SOC and temperatures. You would need to ask the manufacturer what temperature and SOC they used in their testing so you have the same baseline to judge yours from. BUT if its bloated like a football or weighs like a feather – good signs its not Grade A - LOL. If the datasheet does give SOC and temperature at time of testing – and your battery does not meet the requirements within a range of error – then you’re probably looking at a B.

CAPACITY: Another pet peeve of mine. For LiFePO4 batteries – worldwide – the standard testing criteria is 25C with a charging and discharge of 1C. Testing any differently will get you different results then the data sheet because of temperature and charge / discharge variances. Different temperature deviation from 25C on LiFePO4 has a measurable difference on capacity … with that said – often times its minimal but the baseline testing worldwide is at 77F at a 1C charge and discharge.

INTERNAL RESISTANCE: This is an important one – making LFP batteries is complicated – it truly is. Some companies have this down to a science – others – not so much so. TONS of things can go wrong. TONS!! Going from materials to a finalized battery is a complicated 7 step process – and along that step a million things can go wrong – from bad materials to a microscopic tear in the combining sheet to the sheet tearing at the end, to etc etc. IR testing is a good way to see if everything is working on the inside. Again temperature and SOC from the datasheet is required. Most manufactures will suggest an AC internal resistance test but most of the end users like me utilize a DC IR reader. I’m lazy and its quicker and virtually just as accurate ….

SELF DISCHARGING RATE: So self-discharging is calculated by looking at the how fast the voltage is decreasing from its last SOC. As we all know with LFP – its pretty much a flat voltage line from 10-90%. So a battery at 100% state of charge will have a quicker discharge rate then one at 50%. So again – the data sheet is vital to see what the SOC was that they tested at. Now to be honest, YEAH there is a complicated formula they taught us in school and you need to let it sit for 90 days at 50% SOC in a room with a stable temp of 25C and this and that and to be honest – I normally skip testing this … But just in case you wonder anything UNDER 3.51% loss per month is considered GRADE A.

((SIDE NOTE)) – In China MOST GRADE A- cells being sold as GRADE A- is ONLY being sold as A- and not A+ because they have been sitting on a shelf for more than 6 months. Seriously – often times that’s ALL it takes for a manufacturer to drop it from a + to a -. And if a battery is going to last 13.5 to 15 years then 6 months to a year sitting on a warehouse shelf is nothing.

CAPACITY RECOVERY: This one is pretty straight forward – also known as Depth of Charge testing or – DOD. Just do a 100% charging and then 100% discharging and then 100% recharging. If the datasheet says that the Capacity Recovery rate is 100%, and you charge the battery to 100% after a discharge to 0%, then you are fine – if it charges to 98% (for example) then you have issues. Capacity test is how I find 99% of my bad batteries.

Finally a couple of notes from our real life measurements of 1000’s of various batteries….

Note 1.
Using a 280Ah battery as an example:
At 0C we get 85% capacity
At 25C we get 100% capacity
At 40C we get 80% capacity

Note 2.
For the last 1000 LFP batteries we have got in, 11% of my batteries did NOT match the datasheets requirements BUT they were good enough for what we needed. Some were off only by 2-3 Ahs … For example most of the 89% barely made the rated 280Ah and many of the 11% only got between 272-280%. Good enough for me BUT we did not get what we paid for. Being a bored angry Asian girl out in the middle of the West Texas desert, I normally tell Alibaba that if I paid $100 for a battery and its missing 5% of the Ah charge I paid for – then I want $5.00 back. Now multiply that by a 100 “bad” batteries and it comes to real money quickly … and often times I am successful in getting compensation. Most companies would rather pay you a few dollars back then deal with the pain of doing the right thing. AND if we all start complaining then they are less likely to pass B's off as A's.... Remember - they don't get paid UNTIL after the Assurance Deadline passes.

I think that’s about it.

sorry for the rambling.

Thx
 

Bob B

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I'm curious if you agree with what this guy has to say ....

 

wattmatters

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the standard testing criteria is 25C with a charging and discharge of 1C
Thanks for the informative post.

As a suggestion, perhaps include a degree symbol ° when referring to Celcius temperatures so temperatures and charge rates are less likely to confuse a reader learning about such things, e.g.:

the standard testing criteria is 25°C with a charging and discharge of 1C
 

ghostwriter66

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I'm curious if you agree with what this guy has to say ....


NO .... If a "bad" guy is going to fake GRADE B's or below as Grades A's then he is going to go on the Internet and simply find a report (there are 1000's of them) and print it out if that's a showstopper ...

Its like those Chinese sellers that shows all of these battery voltages and IR and this and that when a) voltage means nothing .. and b) they probably have used that picture or clip to you 100X by now ...

Its a roll of a dice -- you do the best research you can - you go off what past ppl say -- you PAY BY CREDIT CARD ... and still sometimes you wind up walking weird for a week ...
 

ghostwriter66

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Thanks for the informative post.

As a suggestion, perhaps include a degree symbol ° when referring to Celcius temperatures so temperatures and charge rates are less likely to confuse a reader learning about such things, e.g.:

I normally would but I am actually riding shotgun out to one of the generator sites today and this iPad they give us so we can have connectivity to the server in the middle of nowhere takes 10 steps to get to the degree simple .... LOL
 

rmaddy

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this iPad they give us so we can have connectivity to the server in the middle of nowhere takes 10 steps to get to the degree simple
Just hold down the 0 (zero) key to get the degree symbol. At least that works when using the English keyboard. Not sure about others.
 

Hedges

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I superscript a lower-case "o"

Sometimes I'll look up symbols and Greek letters, but so much gets lost in the translation. 100 ohm becomes 100W, micro becomes milli ...
 

DJSmiley

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In cases where it really does matter I sometimes just google and copy/paste

Generally, I don't care. If I refer to eg 30C/86F as temperature, I don't see the added benefits of actually properly typing 30°/86F since anyone will know what I mean anyway :)

If I mix it, as in this example, the C refers to both temperature and capacity in a single sentence, I just might add something like 'temp' or whatever the value applie sto.
Example:
the standard testing criteria is a temp of 25°C with a charging and discharge of 1C


Also for eg capacitors, 1000uF will do, even tough it's 1000μF, and for resistance, it's either fully ohm or shorted: 100ohm or 10k

In general, I think my mistakes are more likely errors in English grammer, since English isn't my native language. So there is probably much more to annoy people with my posts than missing a C or ° :cool:
 

ken morgan

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NO .... If a "bad" guy is going to fake GRADE B's or below as Grades A's then he is going to go on the Internet and simply find a report (there are 1000's of them) and print it out if that's a showstopper ...

Its like those Chinese sellers that shows all of these battery voltages and IR and this and that when a) voltage means nothing .. and b) they probably have used that picture or clip to you 100X by now ...

Its a roll of a dice -- you do the best research you can - you go off what past ppl say -- you PAY BY CREDIT CARD ... and still sometimes you wind up walking weird for a week ...
walking weird for a week... Sure you have not spent anytime in the military?
 

ken morgan

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btw for a pc its simple alt 0176 gets you the degree symbol alt 0178 gets you the squared and alt 0165 gets you the yen symbol.. etc. etc. etc. ° ² ¥ memory... its there for a reason use it or lose it to Parkinson's or something worse.
 

chrisski

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What piece of equipment do you use to measure internal resistance?

My google search just turns up normal DMMs and using a 4 ohm resistor With some math. To me, at the single digit milliohm level, does not seem like it would be that accurate. I see pics of test equipment, but don’t see these for sale.
 

ghostwriter66

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Search for a battery resistance meter on eg Aliexpress. Common used one for example is ' YR1035 ' model, around $50 or so

Totally agree ... my choices are a $3000 FLUKE or a $50 YR1035+ ... one weighs 35 pounds - the other maybe 5 oz... but both give me virtualy the same results ... for what I do -- thats good enough ....
 

Gazoo

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sorry for the rambling.
Thanks for your very informative post. The only thing I would like to add is not all suppliers are consistent in what they are selling. Some people have very mixed results who have ordered from the same supplier.
 
Last edited:

wholybee

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yeah on this one when I hold down the zero key I get ... 0000000000000000000000000000000000000

It's highly platform dependent. I suspect someone holding down a key for a different symbol is on a phone or tablet. On a Windows computer there is an included program "Character Map" that will show all the possible characters and symbols, let you copy them to the clipboard, and it will tell you the Alt key sequence. Mac has something similar but I forget what it is.
 

Bob B

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You can also use that "Character Map" document to make your own custom version where you only have the characters you might use .... pin is somewhere handy and copy and paste from it.
 
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