Hi All
Last night my 18650 flashlight died on me. I assumed that the battery was just depleted but today when I put it on the charger (Fenix ARE-C2) it didn't register at all. Zero volts. The same on a different charger. (Nitecore D4). The battery is over 7 years old and is a Nitecore NL186 2600 mah. This is the first time this has happened with these. My inclination is just to toss it.
Are there any things you recommend I try before I toss it out?
Based on how I read your post, this appears to be exactly what I experienced a couple of nights ago, and on another occasion a couple of weeks ago. There was no equipment failure /malfunction involved in my cases, only a failure of the user, as this DA had become distracted by life and lost track of usage of the light since last cell swap / charge. I swapped cells and resumed using the light.
Because the light shut off during what appeared to be normal operation, it was apparent to me that I had simply over-discharged the cell. They are "protected" cells with a safety circuit which opens (shuts off) the output when the cell voltage drops below a designed threshold value to prevent me from discharging them to a level which could damage them or otherwise create a safety issue when recharged. The cells were doing exactly the job I paid them to do (thankfully). Simple operator malfunction.
This 'under-voltage / over-discharge' feature / function in a separate cylindrical cell is generally not auto-resetting, and must be intentionally reset before charging and resuming use of the cell (not unlike a typical 'circuit breaker'). Many chargers have this function. One of mine (Xtar VP2) does this by default when a cell is inserted, as it maintains a voltage across the cell terminals of an idle slot that provides the reset function. Another (MC3000) displays the lack of a valid cell, I then push a button to reset the safety circuit, it displays the open circuit voltage of the cell following reset, and I then push another button to begin charging. I prefer the latter design, because I prefer to be informed.
Most rechargeable consumer electronic devices of course handle this automatically. When the device shuts down, the user plugs in the charger.
In the case of separate cylindrical cells like ours, if one's charger does not provide this function, they may be reset by briefly (single-digit seconds) applying a voltage (in parallel) to their terminals directly. That's often accomplished by simply connecting a normal / charged cell directly in parallel with the one that's tripped (+to+, -to-). I don't need to do this, but I'd just rubber band them together and press the buttons down on a conductive surface, then briefly connect the 2 (-) terminals together w/ something conductive (wire/paper clip/tool, etc.)
Your issue's likely been resolved, but just thought I'd post this for those who might not be familiar with such.
EDIT: If a cell cannot be reset in this way it should be taken out of service, and should NOT be disassembled.
I should also add that these instances I experienced were during non-critical use of my light in a not-critical application.
