That’s not too bad, compared to the ones I got. As mentioned in an earlier message, I got 8pcs. 1pc arrived at around 3.77v, another arrived at 2.0v, and the rest are between 0.1-0.8v.
Since I felt like experimenting, I tried to slow charge them first, until they got to usable voltage (3+ volts). I monitored if the battery’s temperature is getting warmer (some of them did get slightly warm, but not too hot).
Feeling more brave, I decided to charge them up to 4.20v (I use SkyRC MC3000 with temperature cut-off, so in case temperature gets warm, the charging should cut off.
In any case, 3 of the batteries are getting much warmer (40+ degrees Celsius; although being in a tropical country, basically our room temperature would be something like 30+ degrees Celsius basically whole year round). I noticed that those 3 just would not get to 4.20v even as charge current kept on decreasing (Constant Voltage phase of charging). I manually stopped the charging when the batteries won’t charge to 4.20v after maybe 1-2 hours. Did a discharge capacity for all 8 batteries, and about 5 of them only had around 5000+ mAh capacity, while 3 of them had around 6000+ mAh capacity (from full down to 2.50v cut-off at 1Amp discharge current).
Decided to charge all batteries to 3.70v and start checking which ones will self-discharge faster. As noted, the 3 that refuse to full charge, started to self-discharge faster (and actually the battery felt a bit warm to the touch compared to the slower-self-discharging K64). So, it means the batteries high “internal self-discharge” is being translated into heat (I was afraid at this time, because, will the battery vent or explode? I’ve not experienced venting or explosion yet from li-ion batteries before though…)
Anyway, placed the batteries in a non-flammable surrounding and started checking voltage. The fast self-discharge were already below 3.0v within 24-36 hours. While the slower self-discharging K64 took maybe 3 or more days to get to 3.0v. I didn’t try recharging the batteries and stopped monitoring voltage after around 3 days.
On checking, all batteries got discharged further. I want to try testing the batteries again, so I got the 3 “best” K64 (those that self-discharge slowest when I charged them to 3.70v)
So charged them to full 4.20v. They charged to 4.20v without problems. I hadn’t removed the batteries from the MC3000 charger yet, but maybe after an hour , the MC3000’s fan automatically turned ON (meaning it detected a hot battery, even though charging has already stopped about an hour ago or so. I immediately checked and one of the batteries that charged to 4.20v, is getting WARM. This scared me somewhat. Immediately removed the said battery, and I thought to immediately discharge the warm K64 battery using a cheap generic flashlight (so placed the WARM fully-charged K64 battery inside a cheap generic flashlight to drain the battery, set to a low-medium brightness level - I think that generic flashlight uses less than 1 Amp for that brightness setting). It took several hours to drain the battery, at least it’s not warm anymore after getting discharged.
In summary, even the previously “good” K64 (even the one that arrived at 3.77v), it now experiences fairly fast self-discharge (won’t last 1 week before it gets to below 3.0v). Although I just charged them to 3.70v (MC3000 allows ‘storage’ mode and configurable charge/discharge end-voltage setting)…
So, none of the 8 K64 are really “good” as all of them self-discharge fairly quick. It seems that charging them to Full 4.20v is a main cause for the battery getting faster self-discharge issue. (I don’t suggest to test these batteries without monitoring temperature and exercising caution…)