Today, I charged a cheap LiitoKala 21700 cell and the cell died during charging. I never experienced this, so I was wondering if you have.
The model is Lii-40A and the label says 21700 4000mAh 3.7v. The battery was charged with Lii-600 charger. The charging current was automatically selected by the charger at 2A. I usually select the charging current manually at 1A, but today I was lazy and let the charger do its thing on its own.
After about 2 hours, I checked the charger. The charger displayed “NULL”. This was the first time I saw this message when a battery was placed in the charger. So, I noticed something was wrong. I take out the battery and the battery was warm to the touch. I could comfortably hold the battery with my bare hands. I think it was about 40C.
I suspect some kind of protection made the cell kill itself. I think overheating during charging may have tripped it. After about 30 minutes, the cell is still warm. It is not as warm as when I took it out of the charger, but its temperature is way higher than ambient. It currently measures at 32C when ambient is 24C. It looks like the cell is slowly discharging itself.
The voltage was measured around 0.5V when I took it off the charger. After 30 minutes, it now measures 0.2V. What is interesting is that the voltage drops quite rapidly when I place the probes of my multimeter. So, the numbers above are the maximum values each time I placed the probes.
Definitely possible. Especially with a liitokala battery on a liitokala charger. Anything can happen.
I got a liitokala 18650 from Simon at convoy included with my last order and it has a bunch of spelling mistakes all over the wrap lol. Idk what to make of it. Who fakes liitokalas? Or can they just not spell? Capacity and internal resistance check out good enough tho at 1amp. I’m gonna string a bunch of 10w resistors in parallel and series to make a sketchy load tester and see what it does at 5amps.
As I understand it there is essentially a fuse at the top of all cells, some kind of membrane that will rupture if excessive load or discharge is applied.
A cell heats up as much or more because of increased internal resistance than a high charge rate. I charge most of mine at 3A when they’re pretty low and it’s virtually not a problem.
I once had a two cell light quit on me while in use. Checked everything, changed driver, emitter… turned out one of the two matched cells failed. Second was fine and used it as a single for a long time after.
Ten years into this, several hundred cells most getting worked pretty hard. I’ve had about 10 die so far.
You can trigger the PTC or CID when charging. Many cells (but not all) have these. When this happens it’s highly advisable to discard the cell even if its apparently working again later.
That is what I thought as well, but the cell apparently failed during charging.
I am not sure if high-current charging alone destroyed the cell, but it is the only plausible cause for the failure at the moment. I have one more of the same cell, so I will see if I can replicate the failure. However, I think it is likely that some kind of defect caused the failure during charging. I don’t think this kind of failure is common as I have not seen similar failures on this forum.
By the way, the cell was not driven hard at all. The cell was moderately used in Convoy M21C (Cree XHP70.2)and I decided to charge the cell when I observed step-downs on high output levels. That means battery charge levels were low but not to the level close to depletion.
@Limsup … I’m betting (guessing) something just happened to go wrong internally in the battery. I seriously doubt you caused it by charging at 2A, which is only 0.5C.
I have charged numerous batteries (over & over) ranging from 2800 mAh to 5000 mAh at 2A with problems ever (so far ) I would go higher on some of them but 2A is the upper limit on any of my chargers.
It will be interesting to see if you can duplicate what happened. With the other battery. Please do keep us posted & good luck.
) I would go higher on some of them but 2A is the upper limit on any of my chargers.