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Don't keep fully charged Li-Ion in long term storage, they tend to bulge

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james_s:
I don't think they are known for dying quickly if they are treated reasonably, but they have a low tolerance for abuse. I still have numerous LiPo packs that are going on 9 years old now that have hundreds of flights on them and still perform well. I have always been diligent about putting them at a storage charge and I normally store them in the refrigerator over the winter when I'm not flying.

RoGeorge:
From personal experience, Li-Ion have the longest life from all domestic batteries.

- Pb acid batteries, wet or gel (thinking car batteries and UPS batteries) last 5-10 years most.
- NiCd or NiMH (AA or AAA) about 2-5 years, after that the internal resistance grows and make them unusable (for NiMH), while most of my NiCd grown internal short-circuits.  The shorted ones can be pulsed with huge current to burn the internal short-circuits (put a 1.2V cell in parallel with a 12V car battery for a second or so to fuse any internal wiskas), but a couple of days or weeks later they will self-short again.
- Li-Ion can live 10-15 years maybe more, judging by the batteries from the 90's mobile phones that are still working today.  Even the inflated ones still keep 50-70% of their nominal capacity.

The only ones I know to last even longer are some open batteries I've seen in industrial environments, but those used to have their own dedicate room and have been constantly checked/refilled by qualified personnel.  Seen such battery rooms as backup for telephone exchange centers or for control equipment in energy distribution stations near power plants.  One of those battery rooms was 50+ years old and all the cells were still working fine.

Psi:
Often they store them at a voltage that's higher than the "ideal" storage voltage because all cells will self-discharge some percent per month.
Usually 1-2% but it can be higher if the cell has a PCM (like 3-5%).

So it's a trade off. If you charge them a bit higher they will last longer before self discharge takes them so low that damage may occur from undercharge.

So you kinda have to decide, do you want to cause a little damage now to prolong their storage lifespan.
It really depends how long you plan to store them for.

IMHO as long as you store them under 4V it's pretty safe.
So for long term storage I use 3.85-3.90V
Short term storage I use 3.75V-3.80V

It does depend on the chemistry though,  cells designed for very rapid and high discharge are more prone to damage if left fully charged than cells intended for slow discharge.

Siwastaja:

--- Quote from: Psi on January 15, 2023, 09:54:51 am ---Often they store them at a voltage that's higher than the "ideal" storage voltage because all cells will self-discharge some percent per month.
Usually 1-2%
--- End quote ---

Usually much less than that. If you actually measure, that is, instead of reading Battery University or internet forums. But yeah, some cell might just self-discharge by 1-2%/month at 80-100% SOC, at 45degC or something like that.

(I have posted some data in https://www.eevblog.com/forum/chat/lithium-ion-battery-degeneration/msg3217888/#msg3217888 )


--- Quote ---So it's a trade off. If you charge them a bit higher they will last longer before self discharge takes them so low that damage may occur form undercharge.

--- End quote ---

Bullshit. Self-discharge nearly stops at SoC < 50%. If "self-discharge" brings a cell to death via overdischarge (copper dissolution), then it was a very crappy cell. If the cell has internal damage from e.g. earlier overdischarge, then sure this happens, but it also offers a good checkpoint to report broken cell to the user, by refusing to charge.

Does not happen with decent cells.

Now faulty or poorly designed protection modules can consume whatever current. 3-5% of capacity discharged per month is not IMHO acceptable, it's an order of magnitude too much. But for some users / applications, it might be OK. Lazy BMS designers designing packs that self-destruct by misunderstanding the actual field requirements (and assuming large self-discharge is OK) are the plague of the BMS industry, though.

Psi:

--- Quote from: Siwastaja on January 15, 2023, 10:05:23 am ---Bullshit. Self-discharge nearly stops at SoC < 50%. If "self-discharge" brings a cell to death via overdischarge (copper dissolution), then it was a very crappy cell.

--- End quote ---

You can't use the argument "good cells don't do that so you're wrong" when there's loads of crap cells people have to deal with.
Not everyone gets to play with the top tier cells.
Lots of consumer stuff has shit cells with shit PCMs because they are cheap and cause planned obsolescence.

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