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0 pointsMaursault4y ago0 comments

There's more than just the safety aspect, which, again, is to never allow your cells to drop below 2.5V, though dendritic formation is a function of how long the cell's voltage was below that threshold. At 3.6V, your cell is depleted, and I would expect at least smart devices will have low voltage detection and will shutdown at some low voltage threshold if low battery indicators are ignored. To be clear, it isn't the cell dropping below 2.5V that will cause the cell to turn into a bomb, it is afterwards attempting to recharge it that is dangerous. Stop using and never charge a Li-ion cell that's voltage dropped too low. Recycle it at a battery drop (most hardware stores have a battery drop).

The best practices are pretty simple. To get the most life out of a cell (and this is true of Li-ion, NiMH, NiCad, whatever), rest the cells for at least an hour after use and before charging, and after charging and before use. Adopting these rest cycles allows the cell to maintain its capacity. Abusing a cell by never resting it between use or charging will decimate its charge capacity and reduce the amount of amps it can provide compared to when it was new and unused.

Do not store Li-ion cells long term at full capacity, but instead at 3.7V. This is actually controversial, but allegedly (though I do not know why) storing at full capacity reduces the life of a cell.

And of course don't drop your cells, as it can and will cause internal damage, reducing the life of the cell.

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4 comments · 2 top-level

romwell4y ago· 2 in thread

>To be clear, it isn't the cell dropping below 2.5V that will cause the cell to turn into a bomb, it is afterwards attempting to recharge it that is dangerous.Stop using and never charge a Li-ion cell that's voltage dropped too low.

>Do not store Li-ion cells long term at full capacity, but instead at 3.7V.

These are great suggestions, and also they are absolutely impossible to follow given that we have absolutely no access to the sealed Li-Ion cells in devices that we buy.

How would the OP even know what voltage the cells inside his headphones are at? Even with replaceable cells, we can't expect people to have the tools to measure the voltage - unless the device itself displays it.

And even then, if we know that charging a cell after its voltage drops below 2.5V is dangerous, why do we allow chargers that do that (including devices with internal batteries) to be sold to the public?

MaursaultOP4y ago

With experience one can have an idea of what charge is left on a cell. One easy way to gain experience is with a decent Li-ion flashlight. It doesn't take a whole lot of tools to test resting voltage of a cell, a cheap multimeter will do. Modern chargers should be smart, have some function to automatically test for resistance, and refuse to charge a cell with resistance that is too high or if voltage under load is below 2.5V.

Frankly, I am a bit astounded these devices were developed. I'd recommend against wearing Li-ion cells on your head unless you really know the cells, know their age and history.

romwell4y ago

Again, as a tinkerer, I'm happily learning from your comments — thank you!

But the general public can't be expected to know all that without it being even in the booklet that comes with the product.

>Frankly, I am a bit astounded these devices were developed.

Well look at the comments here that say "risk of death is a part of life, deal with it". That kind of attitude is why.

jacquesm4y ago

Lihtium Ion cells are depleted at 3.0V, not 3.6V. The 2.5 is the lower threshold after which you should no longer use the device without replacing the battery. Most if not all BMSs on the market are well aware of these data points and will respond accordingly: hard shutdown at 3.0V, after that they will use a few uA until you charge them and around 2.6V they go into 'deep sleep' which means even indicators and other interaction stops until the device is recharged.

It is very hard to get a device to go below that 2.5V, unless you aim for it by leaving it for many months (and with slightly larger cells years), self discharge at that voltage is extremely low unless the cells have been damaged.

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