I understand that some of the best 18650 cells can last up to around 500 charge cycles, with average ones coming in around 300~400. Of course, an 18650 cell isn’t going to tell you how many charge cycles it has in its history, unlike a laptop battery pack that manages an array of 18650 and can store meta data communicated to a laptop diagnostic program.
In general, at what point do you retire your 18650 cells? I’m guessing that a good sign of a battery underperforming is when the resting voltage notably drops within a specific time period (e.g. 0.5 volts in less than 2 weeks). I don’t really have a need to invest in a specialized battery tester that can show estimated mAh capacity (my consumption of batteries isn’t high enough to justify spending $75~150 on a quality tester that can accurately show this info). So I’m guessing that if an 18650 cell is charged to 4.19v and it can’t stay above 4.16v within 2 weeks, then it’s probably time to retire it. Does that sound about right?
High internal resistance.
If it overheats upon charge or discharge it goes bye bye.
I have had cells that got too hot to hold during charging.
Capacity loss matters but its more of an indication that more capacity loss is coming., If it does what you need at the lower capacity thats great but expect it to lose even more capacity fairly quickly.
It gets overheated during charging is a pretty good indicator.
I had some used laptop pulls that worked great for years but then all started overheating badly.
All of my batteries are older than this, heck i have some that are almost 10 years old (and still testing at near 100% capacity).
I’d love to have your old cells for some testing and use if they are still good.
I have batteries older than 10 years. Does not mean I would recommend it. 3 years and 80% life is gone. There are external factors that a DMM cannot account for.
If they were $1000 each, I would stretch every minute out of them. But not for $5. I have better things to do than try to bring dead batteries from the dead.
When :
A) They self discharge
B) Refuse to take a charge - ( See C )
C) Voltage sag too much after re charging
D) DO a thermal run away … ( Try to explode ) I think I have had two of those over the last 15 or so years . Usually my fault cos I caused a short .
My MiBoxer and Vapcell chargers measure the IR and charge accordingly. So no way I can see them overheating if the chargers are just pushing a few Watts. But I do have noted the IR when new and periodically check. If I see a 50% increase there, I re-test and confirm. Then they are tossed in the low bin (just in case I do need a low valued cell for testing a circuit or light). But that scenario hasn’t come up yet with my better OEMs, only those “economical” pulls from miscellaneous power packs.
Yes, most definitely if a cell became very warm or even hot to the touch, that would be an immediate indicator of a dangerous cell ready for recycling. But do all cells do that once they’re worn out?
As an aside, I found this interesting page where the author claims that when cells go into deep discharge and most battery chargers will reject them, there’s a way to possibly recover them. Bring them back up slowly to the voltage threshold (might be like 3.5v) and a charger will then be able to charge back up to maximum capacity. LINK.
Interesting charger but it would just hide this problem.
I would personally use a regular charger at least occasionally so you can spot this problem on old cells. Aim for 0.33-0.5C charging on this charger so a very low charge rate doesn’t hide the problem.
Below 2.5V cells can start forming internal dendrites, the may be fine once recovered for months or years then burst into flames of these dendrites grow and puncture the cell internally.
So once it goes below 2.5V the cell is done, no matter how old or new.
I use an age based replacement system, not a symptom or status based system. Works for me. A battery can one day save your life so I like to leave as little as possible to chance.
I’ve got ancient laptop-pulls (mostly panny-As), from laptops that were used Every Single Day and probably charged accordingly, and while capacity might be down, they still don’t roast when charging, and have at least half their capacity left.
In low-stress lights, they’re perfectly fine.
I’ll usually charge at 1A, and if the cell doesn’t get too warm, it’s fine in my book.
I have had cells (usually those recycled/rewrapped “free” cells from craplights) that did get quite warm, so nope, they’re gone.
