During the summer sales on AliExpress I decided to buy 16 LiFePo4 cells, since I could save something on the price. The above is what I chose, because the price was very good and it had plenty of positive feedbacks of which the following is but a sample.
I received the packages about 9 weeks after the order, and when I unpacked them, the surprise…
The terminals were not just worn… but in some cases, actually destroyed, the seller had placed new male terminals inside the female receptacles; the cells were all swollen on arrival.
I immediately sent a disappointed message to the seller, to which they replied:
I mean… really?
After this reply, I followed with a long series of messages to say that I had to test the cells further, to decide the amount of refund I needed to ask, and that please I didn’t want to be treated like an idiot.
So, the testing started:
I used a JK BMS, a 100A max current model, with 0.6A balancing current, and a 5.5KW Hybrid Inverter connected to the mains to charge them.
Connections were obviously temporary while I tested, charging was set to 58V, and float to 54.4V.
Soon I noticed a few cells ran away with their voltage, with a delta V reaching quite high values of 300mA, and the BMS kept interrupting the charge until it wasn’t actually charging anymore, I’m talking about a few seconds of charging followed by a few minutes of cooldown.
After this first charge I left the pack alone, letting the BMS do the balancing as best as it could for the night and the whole following morning, and I attached a 2000W heater to the hybrid inverter to test the capacity…
A whopping 128AH capacity (less than 50% of declared) reported by the BMS before one of the cells repeatedly hit the lowest voltage, making further discharge impossible, and needing to disconnect and reconnect the battery leads from the inverter, otherwise it couldn’t start because of a short circuit detected by the BMS. A royal pain.
So this time I tried charging again with the hybrid inverter, after which I intended to to a top balance with a couple of bench power supplies…
The usual #15 and #16 cells kept stopping the BMS because of overvoltage, so I made two large parallel setups, 10P for the 10A power supply, and 6P for the 5A power supply, and left it for a couple of days, after which I built the series again and started charging once more, this time helping the balancing manually, by using a contraption made of 4 parallel 2ohm resistances submerged in water to cool them down, to drop the voltage on the worst cells, many many times… only to repeatedly hit the overvoltage limit on the BMS for #15 and #16 no matter how often I fixed their voltage with the contraption.
Not only this, but the cells became even more bloated after only a couple of charge cycles!
Then the idea came to me, set #15 and #16 in parallel! It would become a 15S battery, still with a usable voltage by the inverter, and maybe I would make up for the limited capacity of the last two cells.
Even like that, and even while using the contraption to cut down the voltage, repeatedly, #15 and #16 in parallel would STILL trigger the overvoltage protection.
Being desperate at this point, I then added #5 to the parallel arrangement since it was the one always jumping higher with the voltage… and the 3 cells in parallel at the end seemed to hold it, while the inverter could still manage with the voltage of a 14S, until YET ANOTHER cell started triggering the overvoltage protection; keep in mind the contraption was still being used to taper the overvoltage on single cells.
Then I said, to hell with it, let’s restore the 16S and now also let’s play a harder game, by charging single cells at the same time with the two bench power supplies.
I played wack-a-mole this way placing the alligator clips here and there depending on where the BMS app told me the lowest voltage cells were, until I got fed up with it.
Currently, I rebuilt two parallel 10P and 6P strings to charge once more overnight with the power supplies, after which I’ll try my Atorch DL24 to test the cells and determine the internal resistance of each.
There are still almost 20 days to go before buyer protection ends, but I cannot endure this much longer. I need to make an estimate of the refund I have to ask.
Continuing from where I left off, I made a single chain of 16 parallel cells, and applied the power supplies at both ends, and took a long time top balancing to 3.6V until the current from the bench supplies was negligible:
I then used the builtin function of the Atorch DL24 battery tester to measure the internal resistances of all the cells, by running them at 0.5A for 1 minute, and noting down the last value the DL24 showed for internal resistance right before the minute was over:
The measured resistances (in milliohms) were as above, with the smallest and largest values reporting the highest current the cell could withstand. Not very good values, at all.
I once again assembled the 16S configuration, and the bloating got even worse:
I had by then also labeled each cell with an identifying number.
I waited overnight to let the cells “rest”, and this was the result:
Then I started once again the discharge test:
I attached the heater to the now top balanced cells expecting great results!
Discharged overnight until BMS killed the process because of cell #3 in undervoltage protection, rebooted the inverted in the morning to try and squeeze out a little more, still under 170AH! And this time, you can see how all the other cells are still around or below 3.1V, which means that they are pretty much depleted anyway, given this is the discharge curve of a LiFePo4:
I marked the 3.1V SOC for the 3.6V charge voltage; this means that all those cells were already depleted anyway when #3 was going in protection, no more juice can be squeezed from the pack.
But I’m really thorough, so I did another full charge and discharge cycle, this time only using the inverter since the cells were already top balanced. As usual the charge stop because #3 hits the overvoltage protection, but all the rest are still basically 100% charged, as per image above (check the 3.4V mark); the discharge stopped also because of #3, but same as above, the others are still depleted at ~3.1V.
Less than 170AH it is, no doubt.
And for some interesting facts, during the following multiple-section recharge, the cells got really balanced:
From 0 to 1mV of delta! They are indeed a cozy bunch, except #3 which likes to spoil it for all the rest, but this pack is a 165AH pack , NOT a 280AH one.
What’s more curious, the seller, even after giving proofs of the defect, started asking me to test a single cell instead….
At this point, I don’t think I’ll follow this request, as it makes no sense to me and I don’t want to waste time, and also unbalance all the set, since by testing just one, after this I will have to do yet another top balance with all the 16 cells in parallel. No thank you. It won’t help anything anyway.
I did I third discharge/capacity test, and results are clockwork at 166AH:
No more tests, it’s settled, I’ll open a dispute with this data, there are plenty of proofs.
UPDATE: I did decide to test a single battery just for fun, I picked the best out of the bunch, #6 which you can see above that has the lowest voltage when pack is charged, and the highest when pack is discharged.
I singled #6 out and topped it to 3.61V, then used Atorch DL24 to test it down to 2.7V (why no 3.65-2.5? Because it makes no sense stressing the battery for, what, 1% more capacity?)
Here are the results.
Best cell is 186Ah, a far cry from the promised 280Ah.
I told the seller the results of this test, I also opened the dispute.
The seller’s response to the private message was “you didn’t test in standard conditions” (what are standard conditions? Using their fairy testers that report double the real capacity?), and response to dispute, where I posted, among others, a picture with clearly visible destroyed electrodes, bulging, and crappy covering, was “We only provide brand new batteries, bulging is because of incorrect test conditions and because buyer did not compress the cells”.
DOUBLE-U TEE EF.
This person has no trace of shame in this world.
I am currently in advanced dispute with the seller, and waiting for AliExpress to make a decision based on my indisputable video proof (at least I think), there are hidden scratched QRs under the replaced battery covers showing they were ONCE 240AH (not even 280AH), but I couldn’t resist yelling at the person I’ve been talking with: