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If the voltage of a lithium-ion cell drops below a certain level, it's ruined. Lithium-ion batteries age. [Source]

As an owner of quite a lot of expensive mobile devices (lots of Apple stuff for example) I wonder... what if I, say, put my Airpods in a drawer at, say, 3% charge and "forget about them" for a few months?

Li-ion: 5% in 24h, then 1–2% per month (plus 3% for safety circuit) [Source]

Will my device be unusable? As I understand it I won't be able to charge it anymore?

Also: How does Apple (or any other manufacturer) make sure that devices in warehouses etc. don't "die out" during the time they're in there? I know that Apple devices usually come out of the box at least partially charged, but I assume Apple doesn't charge the devices to 100% anyway. But what if the charge drops below "0%" (or: the 'certain level' from above quote)?

Also: what is "ruined"? The above quote implies the cell being unusable, beyond repair, FUBAR. However:

The protection circuit turns off and most chargers will not charge the battery in that state. A “boost” program applying a gentle charge current to wake up the protection circuit often restores the battery to full capacity. [Source]

and

Some battery chargers and analyzers (including Cadex), feature a wake-up feature or “boost” to reactivate and recharge batteries that have fallen asleep [Source]

Would such a 'wake-up' be available in consumer products (laptops, phones, earbuds, whatever) or would this be put only in industrial stuff?

Lithium-ion batteries age. They only last two to three years, even if they are sitting on a shelf unused. So do not "avoid using" the battery with the thought that the battery pack will last five years. It won't. [Source]

Is that information outdated? I have had quite a few mobile devices over the past decade(s) that lasted much longer than that.

I'm trying to make sense of a lot of sources that all seem to contradict each other one way or another.

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  • \$\begingroup\$ Software reported "battery percentage" != state of charge. Still, keep them at 80 % charge (reported or real) for maximum life. \$\endgroup\$ – winny Nov 8 '17 at 14:33
  • \$\begingroup\$ Software reported "battery percentage" != state of charge Hence the quotes on "0%" and 'certain level' reference). I'm aware the reported percentage and actual charge differ; I'm talking about actual percentage/charge, not reported. Thanks for pointing this out though! \$\endgroup\$ – RobIII Nov 8 '17 at 14:36
  • \$\begingroup\$ There are variety of chemistries in Li-Ion family, and variety of technologies to make internals,foils/barriers. Plus electronic "protection" varies on the top of this. So the results vary. Voting to close as "too broad". \$\endgroup\$ – Ale..chenski Nov 8 '17 at 14:54
  • \$\begingroup\$ Check the StackExchange EE for keyword "overdischarge", you will find plenty of information and opinions. \$\endgroup\$ – Ale..chenski Nov 8 '17 at 15:03
  • \$\begingroup\$ Check the StackExchange EE for keyword "overdischarge", you will find **plenty of information and opinions**. That's the problem; I'm having trouble making sense of all the information and opinions and all the information I find only raises more questions. \$\endgroup\$ – RobIII Nov 8 '17 at 15:05
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If the voltage of a lithium-ion cell drops below a certain level, it's ruined.

That statement is a bit short sighted, it depends on the actual type/brand/model/chemistry (there are several Lithium based types) if this is true. According to tests by BigClive (sorry, I cannot recall exactly in which video he mentions this) some batteries can be completely discharged (0 Volts), charged again and then appear to still have their full capacity. Note that the "fully discharged" state did not last long (hours or days perhaps).

Lithium-ion batteries age

That is true but also depends everything I mention above and also how you treat the battery. For example in some military applications Li-Ion cells are charged not up to 4.1 - 4.2 V (like in many consumer products) but to 3.8 V or less. This places less stress in the cells making them last longer.

but I assume Apple doesn't charge the devices to 100% anyway

That will actually be the battery manufacturer producing the batteries in such a way that they are at around 40% to 60% charge when finished. They're not charged or discharged as that takes too long! The charge level can be set by using the proper ratios of chemicals during production. Same as non rechargeable batteries are made to have 100% charge.

If you want to store a device for some time, I suggest charging the battery to a value between 40% to 70 % (my rough estimate). Then if possible remove the battery!

If removing the battery is not possible make sure that the device is switched off and store it in a location where it cannot get very hot or cold.

To protect against fire and overcharging (when the charging circuit in a product breaks) nearly any device will have a battery protection circuit. This will simply disconnect the battery when the battery is in danger. I am quite sure Apple devices have this.

BTW, this does not protect against manufacturing issues with batteries which is often the cause of batteries catching fire.

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  • \$\begingroup\$ BTW, this does not protect against manufacturing issues Manufacturing issues aside, ofcourse 😉 Thanks for answer though! Much appreciated! \$\endgroup\$ – RobIII Nov 8 '17 at 14:48
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I don't think all spectrum of OP questions can be answered within EE site, but I'd like to address the following:

The protection circuit turns off and most chargers will not charge the battery in that state. A “boost” program applying a gentle charge current to wake up the protection circuit often restores the battery to full capacity. [Source] and

Some battery chargers and analyzers (including Cadex), feature a wake-up feature or “boost” to reactivate and recharge batteries that have fallen asleep [Source]

This is just an inflated piece of baloney. The situation is simple: when a battery gets discharged below certain limit set by protection circuitry (say 2.9 or 2.5 V), the circuit disconnects the battery output. The terminal would show "zero voltage", which looks like "dead". However the INPUT path is there. So if you apply a precharge current (usually 100-200 mA), the cell (behind the circuit) will charge up above the cut-off threshold of it, and battery "wakes up". There is no need in any special secret "wake-up" or "re-activation" tools to do so.

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At Battery University, Safety Concerns with Lithium Ion (the last source, at the bottom), the following is said:

...Li-ion must not dip below 2V/cell for any length of time. Copper shunts form inside the cells that can lead to elevated self-discharge or a partial electrical short. If recharged, the cells might become unstable...

Therefore, before you try to rehabilitate a Lithium ion battery, see if you can figure out how to test the actual voltage of the cells inside, because it may be a safety issue if any cell has fallen below 2 volts for any length of time. This may have caused the beginning of copper crystals, though I'm not sure whether they are more like Crystal Dendrites, or more like the Crystalline Whiskers which we still don't understand. The whiskers are actually amazing, they look almost alien, and like they've been extruded from the surface. When a tin whisker occurs, it conducts significantly better as a crystal than a normal wire does, creating a very effective short. The same would be true of a copper crystal.

If a cell falls below that 2 volt mark, an initial deposit (or many) might have been started, that don't immediately lead to what the industry likes to call "venting with flame" or "rapid disassembly" which would be similar to certain fireworks going off. It may take many charge/discharge cycles for those crystals to grow to the point that they pierce the separator, cause short-circuit and possible catastrophic thermal self-destruction.

Information sources:

The first one, a transcript of a video by Jeff Dahn of Dalhousie University -- Why do Li-ion Batteries die and how to improve the situation., is a video I have watched numerous times. In it, he shows why and how our Lithium ion batteries die, how the manufacturers are developing additives to prolong the cell life, and how temperature and slow charge and discharge times cause the premature death of cells in the Nissan Leaf. Finally, he explains a new method of microcalorimetry Dalhousie U. has developed with him to test these new additives in a reasonable time, which they have not been able to do before. Anyway, stuff I learned from his talk leads me to say that, #1, charge your cells to only 4.1 volts, and...

If you want to not use your Lithium ion batteries for a long time, charge them to half their voltage (I would go for 60% to 70%), and put them in the refrigerator, and they should keep for a long time. Here's the excerpt from the talk:

Question 9: [unintelligible], Question 9: Response, Keep it as cool as possible at all times. Put it in the fridge at night, then it won't bother you while you're sleeping too. [laughter] Added advantage. No but I'm serious - if you keep any battery as cold as possible it will last longer. So any lithium ion cell, you should keep in the fridge when you're not using it, it will last longer. If you don't charge to a hundred percent that will help. But you know temperature is a bad actor - keep in the fridge.

Hope this helps.

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