I had a sneaking suspicion the K64 would have QC problems. Especially since 1. Vapcell does not own their own factory 2. Nobody else is producing a battery with these specs.
To their credit, it has to be tough to design and manufacture a new high discharge cell with increased capacity.
The F14 doesn’t seem to have the same problems probably because only capacity increased. Probably easier to rework existing technology to increase capacity but not both at the same time (high discharge + increased capacity).
Hopefully the F14 stays around, great for Convoy lights since they can’t pull more than 3A.
Interesting, I had a bunch of Vapecells arrive yesterday 2 of which were K64’s and they were perfectly ‘storage’ charged. 3.76v & 3.84v. I drained one down to 2.8v then charged it and got well over 6k mAh’s like 6250mAh. The vapecelll INR21700 4200mAh cells which are the Mollicel 4200 30A continuous discharge had a clear wrapping over the cells which I thought was clever protecting the contacts. But so far I like those K64 cells and the little 18350’s with 1400mAh tested well (T14), I measured over 1400mah when charging but are only 4A. But to be honest I’ve been pretty happy with Sofirns cells like their 4K/5K 21700 and I have a bunch of their 18650’s which have been decent. Much cheaper too.
Having unequal storage voltage shows there’s still a voltage instability problem. Every single Samsung, Panasonic, Sony, and Molicel have been exactly the same voltage across 500+ cells.
Roughly 40 of the 120pcs Vapcell K30 that were okay in my order were a solid 3.71v, the other 80pcs were 3.68v+, and the remaining were even as low as 1.78v (got a refund on 20pcs of the worst)
Measure internal resistance (requires some equipment to compare between resting voltage and voltage under load) and compare against other batteries of the same make and model and/or against the datasheet (if there was one available).
Measure internal impedance (requires an impedance meter like Vapcell YR1030/1035 or SM8124A) and compare against other batteries of the same make and model.
Charge the battery to a certain value (maybe "storage voltage" around 3.6V - 3.8V would be best?) and observe any sagging in resting voltage over the course of let's say 14 days or 30 days. Cells of good quality should keep their voltage rocksolidly stable. Those with a quickly dropping voltage may have some issues concerning their electrodes inside but I can only guess.
Batteries below a certain resting voltage (IDK, 3.0V or maybe lower than this) should not be charged at all and considered as defective?
I wonder how safe it is to run lithium-ion batteries with a high self-discharge rate. I know that some chemistries have a rather high self-discharge rate but I only saw these in NiCd or NiMH cells before. A lithium-ion battery is a whole different thing, I guess.
BTW, I have (among other batteries) six K64 batteries incoming. They are probably still en route to Europe or being checked by customs (who knows). I will be happy to carry out steps 2 and 3 and report about their status as soon they have arrived.