I recently bought a couple of 26650 cells branded with “Dolidada” at this store on Aliexpress. According to the specs on the seller’s webpage this cell should have a capacity of at least 5.500mAh with a discharge current of 20A. Usually, these cells were rewrapped high current Keeppower cells with up to 6.000mAh. Apparently, I was unlucky to get cells from another batch with different specs underneath the shrink.
I ran a C-D-C test with 0,5A of discharge current. The picture indicates the third stage of the cycle, i.e. cells are being recharged again. The test revealed that these cells only have little more than 5.000 mAh at low discharge currents. So, using these cells in a typical flashlight scenario with 7-9 amps would mean to have far less capacities than 5.144 mAh.
Is there any rule of thumb I can use for orientation when it is justified to raise a complaint against the seller for delivering poor quality cells? What are your experiences? I am totally clear about the fact that there is always some kind of variation in terms of capacity but these cells actually seem to be different from what they are supposed to be. I doubt they can even sustain a discharge current of 20 amps.
How would that proof have to look like? Is a picture or a youtube video showing the measured capacity sufficient? It will be hard to proof anything above 2A discharge current for I do not have the right equipment to show the effects of high discharge currents (e.g. voltage drop).
It’s a Zanflare C4, actually. However, I personally disagree to accept nearly 500mAh of capacity missing, especially at such low currents. But that was actually part of my question. Is there a normal percentage of variation for battery capacities? All my 18650 cells have significantly more capacity than stated, e.g. Samsung 30Q with 3.200-3.300mAh instead of 3.000mAh.
It seems I drew a blank in the Chinese battery lottery which brings us to the wise saying “You get what you pay for”. :FACEPALM:
Okay, this kind of calculation helps me to think about my options. For sure, these cells can still be used and they might work fine in low current scenarios but I don’t think they will be as good as those “Keeppowers-In-Disguise” cells former buyers have found in the past.
I can also doublecheck these values with my MC3000, just to be sure. I know that slot #2 always indicates a bit more capacity than the other ones but here I have only used slot #1 and #4. If my C4 indicated too high values with 30Qs it would mean that the actual capacity of the Dolidada cell is even lower.
Just to try and find out the capacity discrepancies, I am throwing into the fray this equipment
I am now charging my 30q, using my MiBoxer C4-12, manually set to 1A.
My iCharger already set to .20a discharge rate, terminal voltage cut-off at 2.80v, waiting for the 30q to be discharge tested after fully charged (photo above), to mimic the settings of Flash Tom’s Zanflare C4 and find the result differences that might lead to a comparative conclusion about the results of his tests of this Dolidada cell.
Discharging has started: .20a rate, 2.80v terminal voltage cut-off (hoping no power failure tonight for such a long session) Resting, sharting voltage after a short rest: 4.14v
Discharge capacity after 10 hours, 4 min. is 2,041mah, @ .20a rate, 3.49v remaining at this juncture:
Edit: This photo is no longer useful as there was a short power failure probably in the thirteenth hour, so the whole process of charging, etc. will be repeated. Ouch!
New session after aborted test due to power failure:
At this juncture, it’s 2824mAh, 2.84v (cut-off at 2.80v), elapsed time: 13h, 55min.
Discharging “DONE” after 14h 07min: capacity: 2860mAh. Discharge rate: .20A
Note: While the charging exactly ended at 2.80v, when I took the photo, the cell was already recovering (at 2.82v) and rapidly going up to it’s nominal, resting voltage (around 3.5 to 3.7v on healthy cells IIRC)
Frankly i think you are lucky to hit 5000mAh with these Dolidada cells!
From what i can tell from the vendor’s page, they look like those Liitokala 50A cells which are not bad - certainly not “lemon” cells.
The last 26650 cells i bought where high drain KP 6000mAh which tested around 5500mAh 5700mAh. No big deal to me.
It’s up to you to start a dispute… but when you buy funny name cells from china for less then $10 a pair, you should be prepared to be disappointed. But in this case the cells look very decent for the price. If you look around you’ll find reports of sand filled 18650 cells that tested at less then 1000mAh…
I think using buyer protection on such a small discrepancy in capacity is inappropriate. You weren’t buying a name-brand cell, so you can’t call this a “fake” cell. Perhaps they did change suppliers, but that’s the risk you take if you don’t buy a name-brand. You might have a point if the cell is nowhere close to a 20A cell, but you’d have to do proper load testing for that. And any cell will not deliver its rated capacity at high load.
Try the cell in the light you were planning to use it in. See if the battery gets abnormally hot. If not, then you can probably use it.
At what discharge current did you test your KP 6000 cells? I’m a bit surprised for KP cells are known to exceed their nominal capacity printed on the shrink. However, thanks for sharing your point of view.
I agree with you. I’ll see if I can test it in of my high drain lights (Rofis MR70, ThruNite TC20) for any suspicious behaviour. My intention was to get cells with the same capacity and same iR to work in serial mode (e.g. 2s configuration).
For cells to be used in series, always order them at the same time from the same place. That way, if you get under-performing cells, they’ll at least be matched. Better two underperformers, than one good cell and one underperforming cell.
Personally, it would not be worth my time and aggravation to try to raise and manage a complaint over a couple of cells that fall a little short of the advertised specs. Move on and buy name brand cells next time.