Two different grades of the same battery in one pack?

[Gorillazilla]

A box arrived today from https://eu.nkon.nl/...

A veritable sea of Cells, and perhaps the first problem in my car replacement Ebike build.




It looks like they have sent me two different grades of cells...

about 6 Boxes of C Grade, and 6 Boxes of D grade. I've checked and the cells inside the boxes are indeed the different C and D Grades.


Will this be a problem with them all going into the same battery pack? I will only be using around 60% of the capacity to maximise total what Hours out battery life. Charging to 80% and discharging to 20%

Should I send them back and ask they send me all the same grade and date code?

 

[DogDipstick]

I've checked and the cells inside the boxes are indeed the different C and D Grades.

Do you know the difference in the two? What is the difference?

Did the purchase come with the QR codes blocked out like that? Did you buy from a good supplier? Is that like 600 18650s?

 

[Gorillazilla]

Do you know the difference in the two? What is the difference?

Did the purchase come with the QR codes blocked out like that? Did you buy from a good supplier? Is that like 600 18650s?

A quick google search didn't turn up much on the difference between cell grades, They came with the QR codes on the boxes Blocked out, But NKON is as far as I can tell a reputable seller that only sells genuine cells.

In fact, it's mostly only NKON.nl mentioned when people ask for the best most reputable 18650 suppliers.


They do have the QR codes printed on the steel casings of the cells, visible under the shrinkwrap

There's 350x 18650 cells there for a 14S 24P pack with plenty of cells left over for calendar aging capacity testing and comparison to the main pack and small side projects




EDIT: I did find a little information concerning cell grades

" " For lithium-ion batteries, nominal values are used for factors with variability to distinguish them from real or actual values. For example, 18650 battery manufacturers have levels of tolerance for the capacity of their batteries. It is impossible to refine the materials and processes so exacting as to produce 18650 batteries with capacities within a single milliamp hour. That is why even within Grade A 18650 cells are Ranks A and B, the latter with a capacity 10-30 mAh less (in application this difference usually only matters when putting cells in a series). " "

From this site. https://batterybro.com/blogs/18650-wholesale-battery-reviews/32496579-comparing-panasonic-18650-bd-vs-panasonic-18650-be

 

[john61ct]

C&D are really rejects

did you intend to buy them?

Were they priced at least half cheaper than Grade A?

And no not a great idea to mix

 

[liveforphysics]

I've never seen C and D grade cells escape a cell manufactures scrap recycling process.

Cells that are already 5 years old would be expected to have some impedance climb sitting unused for that long.

I would test them before building a pack to be sure it can achieve your expectations.

 

[john61ct]

Staff at Asian OEM factories sneak stuff out the back door to the dodgy resellers that dominate Ali.

Same with counterfeit production runs, re-wrapping secondhand cells etc

Sometimes the quality turns out not so bad, but certainly not consistent.

If you dabble with such lower tiers, better be paying a small fractiin of what the good stuff goes for.

Personally I'm surprised a vendor with a brand rep like nkon would touch such products with a ten foot pole, even if truthfully advertised.

Hopefully they have good standard go/no-go testing before shipping.

 

[Gorillazilla]

C&D are really rejects

did you intend to buy them?

Were they priced at least half cheaper than Grade A?

And no not a great idea to mix

I didn't intend to buy rejects for sure, They were not advertised as such. They were €4.05/£3.40/$4.56 Each cell, though reduced to €3.70/£3.11/$4.17 because I bought over 180 of them.

Does the "Rank D" actually mean they are Grade D cells, or just different ranks of Grade A?

Because what is mentioned here:

" " For lithium-ion batteries, nominal values are used for factors with variability to distinguish them from real or actual values. For example, 18650 battery manufacturers have levels of tolerance for the capacity of their batteries. It is impossible to refine the materials and processes so exacting as to produce 18650 batteries with capacities within a single milliamp hour. That is why even within Grade A 18650 cells are Ranks A and B, the latter with a capacity 10-30 mAh less (in application this difference usually only matters when putting cells in a series). " "

From this site. https://batterybro.com/blogs/18650-wholesale-battery-reviews/32496579-comparing-panasonic-18650-bd-vs-panasonic-18650-be




Here's the link to what I bought https://eu.nkon.nl/rechargeable/li-ion/18650-size/panasonic-ncr18650pf-3-7v-2900mah.html

 

[99t4]

Yes Nkon has had a good reputation among ES members. Can you ask them your questions?

 

[Gorillazilla]

Yes Nkon has had a good reputation among ES members. Can you ask them your questions?

I'll Ask them, and direct them to this thread to see if they can help clarify matters.

 

[Farad]

Yes Nkon has had a good reputation among ES members. Can you ask them your questions?

I'll Ask them, and direct them to this thread to see if they can help clarify matters.

Did you get a response from Nkon?

I'm looking for a reliable supplier to the UK. Did you have to pay import duties on these?
I've used 18650.co.uk before and they were OK and they currently have these for £2.99...

https://wholesale.18650.uk/product/panasonic-ncr18650pf/

Or the higher capacity NCR18650BD for £3.05...

https://wholesale.18650.uk/product/panasonic-ncr18650bd/

Not quite as cheap but maybe not so far off once the post Brexit levy is added? :?

 

[Gorillazilla]

Did you get a response from Nkon?

Yes, turns out they were not rejects. Just different ranks, there's very little difference between A B C D apparently. Just 30Mah or so between ranks.

And no, I didn't pay any duty on that huge order from Nkon


I did pick up a YR1030 battery internal resistance tester though (highly recommended on many forums as being one of the best, and best value), as Arjan from Nkon told me that minimising internal resistance differences within parallel groups is more important than slight capacity differences, as explained in this article https://www.sciencedirect.com/science/article/abs/pii/S0378775313019447

 

[Farad]

Thanks for passing that on. I've built a couple of low power batteries for ebikes but am now planning a mcycle conversion with 72v or 96v and high amps. A different league where I need to research more before committing to a specific design. Must admit I hadn't considered the need to match internal resistance so something else learnt today :thumb:

I'm surprised that there were no customs duties or handling fees on an EU purchase, I thought they would now be treated the same as China/Ali Express. You must have researched before making your purchase, are you confident that similar transactions would always be exempt as an unexpected charge would more than wipe out any gains?

Thanks again for the tip.