> On Dec 22, 2022, at 6:30 PM, Will Cooke via cctalk <cctalk@classiccmp.org>
> wrote:
>
>
>
>> On 12/22/2022 4:34 PM CST Chuck Guzis via cctalk <cctalk@classiccmp.org>
>> wrote:
>
>>
>> That's not to say that Li-ion cells are without their quirks. I
>> recently almost discarded a AA-sized 14500 cell because the output
>> voltage had suddenly dropped to the point where none of my chargers
>> would even see it. So I put it on a corner of my workbench against the
>> time when I had accumulated several and could turn them in for
>> disposal. A couple of days ago, I picked up the cell and checked it
>> with my voltmeter and it read 3.5V. Put it in the charger, and slowly
>> charged to capacity. What happened during the month or so that it sat
>> on my workbench, I cannot say.
>>
>> --Chuck
>
> A VERY large percentage of LiIon batteries have a protection circuit built in
> to prevent over-discharge. Even a lot of the "standard" cell types (e.g.
> 18650s) The circuit disconnects the battery from its terminals if the
> voltage drops too low, showing near 0 volts out. If it just barely meets the
> cutoff, it may recover enough to re-activate the circuit, making it possible
> to recharge it. Often, you can open the case, skip over the circuit board to
> access the battery cell directly, and add a small amount of charge to
> reactivate it. Then it will work normally. I've done this a few times.
>
> Will
That rings a bell. The battery chapter I mentioned says that Li cells need
protective circuits, so any loose cells or battery assemblies you buy have that
built-in as a standard component. The only people who get to see bare cells
are those who assemble their own battery packs. So car makers take in 18650
cells by the shipload, without built-in protection because they supply that
protection as part of their packs. But when ordinary civilians buy lithium
cells we get protected ones.
paul
