Author Topic: Battery Li-Po storage mode  (Read 833 times)

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Offline tiago1986

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Battery Li-Po storage mode
« on: June 16, 2021, 08:48:32 pm »
Battery Li-Po in 3,85v is storage mode or no?
 

Online Siwastaja

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Re: Battery Li-Po storage mode
« Reply #1 on: June 17, 2021, 08:14:19 am »
It's good enough.
 

Offline tiago1986

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Re: Battery Li-Po storage mode
« Reply #2 on: June 17, 2021, 09:48:11 am »
what is the full voltage range of lithium or LiPo battery for long term storage?

what are the self-discharge benefits of storing at this voltage?

if i stored the Li-Po near 100% or at 100% for a few months then the battery lost its useful life, lost the 2000mah it supports?
 

Online Gyro

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Offline tiago1986

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Re: Battery Li-Po storage mode
« Reply #4 on: June 17, 2021, 03:43:29 pm »
my bp5l and bm20 batteries are stored at 3.8 or 3.85v is this not recommended for long term storage? do I need to reduce the charger further?

what are the self-discharge benefits of storing at this voltage?

if i stored the Li-Po near 100% or at 100% for a few months then the battery lost its useful life, lost the 2000mah it supports?

 

Online Siwastaja

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Re: Battery Li-Po storage mode
« Reply #5 on: June 17, 2021, 04:47:30 pm »
Really really depends on the cell, I measured some and for example Sonys very exceptionally good and Samsungs and LGs while good not that good. I posted some results in https://www.eevblog.com/forum/chat/lithium-ion-battery-degeneration/msg3217888/#msg3217888

Put in numbers, assuming your cells are closer to the LG numbers than Sony, near 100% at your elevated room temperature (like 30-35 degC) would lose 6% of capacity per year. So a "few months" would be what, maybe 2%, or dropping from 2000mAh to 1960mAh.

But this is assuming your cells are of good quality. As they are likely some cheap counterfeit crap, all bets are off. They may be as good as the LGs I measured, or they might be significantly worse.

From the Samsung 29E data I posted, you can also see that a fully charged cell loses 6.1% of capacity per year in warm temperature, but one stored at 50% charge (3.6V) only loses 0.9%! You can also see that cell stored at 4.0V instead of 4.2V won't get much extra life, but at 3.6V the difference is huge. Sadly I didn't test at 3.8V. It's going to be better than 4.0V but how much better, I don't know.
« Last Edit: June 17, 2021, 04:50:02 pm by Siwastaja »
 

Offline tiago1986

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Re: Battery Li-Po storage mode
« Reply #6 on: June 18, 2021, 09:39:51 am »
Really really depends on the cell, I measured some and for example Sonys very exceptionally good and Samsungs and LGs while good not that good. I posted some results in https://www.eevblog.com/forum/chat/lithium-ion-battery-degeneration/msg3217888/#msg3217888

Put in numbers, assuming your cells are closer to the LG numbers than Sony, near 100% at your elevated room temperature (like 30-35 degC) would lose 6% of capacity per year. So a "few months" would be what, maybe 2%, or dropping from 2000mAh to 1960mAh.

But this is assuming your cells are of good quality. As they are likely some cheap counterfeit crap, all bets are off. They may be as good as the LGs I measured, or they might be significantly worse.

From the Samsung 29E data I posted, you can also see that a fully charged cell loses 6.1% of capacity per year in warm temperature, but one stored at 50% charge (3.6V) only loses 0.9%! You can also see that cell stored at 4.0V instead of 4.2V won't get much extra life, but at 3.6V the difference is huge. Sadly I didn't test at 3.8V. It's going to be better than 4.0V but how much better, I don't know.
Do you recommend that I discharge the battery down to 3.6V for best long term storage? today the xiaomi BM20 and BP-5L are stored at 3.8V or 3.85V

even if my battery is fake is its self-discharge lower if I keep it at 3.6V?
 

Online Siwastaja

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Re: Battery Li-Po storage mode
« Reply #7 on: June 18, 2021, 09:45:08 am »
If you can do it easily, go on and discharge to 3.6V. If it is a struggle, don't bother, it's good enough at 3.85V.
 

Online beanflying

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Re: Battery Li-Po storage mode
« Reply #8 on: June 18, 2021, 09:48:23 am »
Don't stress to much you are in the ballpark.  :)

When I was flying a heap my fleet of LiPo's Packs from 2-6S (50-60 'I think' :-DD) were stored full. Currently due to plague induced low level/nil flying they are stored around 3.8V/cell. As to past high voltage being an issue to cycle life or capacity :-// a bunch of my packs are at least 6-7 years old and some are now over 10 years old.
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Offline Psi

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Re: Battery Li-Po storage mode
« Reply #9 on: June 18, 2021, 09:54:25 am »
All lipo's will self-discharge somewhat, so better to store it a little above 3.8V

3.85V is totally fine.

Most consumer products that include a lithium battery ship from the factory charged to 3.9V.
The goods have to last for quite a while in transport and sitting on the shop floor. They only get their first charge once bought by a customer and that could be a year later.
It would be bad if the battery had self-discharged so much that it started damaging the cell before the customer even bought it.
« Last Edit: June 18, 2021, 09:56:07 am by Psi »
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Offline tiago1986

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Re: Battery Li-Po storage mode
« Reply #10 on: June 18, 2021, 10:05:24 am »
my doubts the Li-Po self-discharge at 3.6V is slower than the Li-Po self-discharge at 3.85V???

my batteries are xiaomi BM20 and a copy of Nokia BP-5L
« Last Edit: June 18, 2021, 11:40:12 am by tiago1986 »
 

Online Siwastaja

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Re: Battery Li-Po storage mode
« Reply #11 on: June 18, 2021, 11:47:06 am »
Yes self-discharge is slower at 3.6V than at 3.85V, but it's already very slow at 3.85V, at least compared to 4.20V.

You don't need to leave margin "in order not to self-discharge into death", that's a myth which only applies to cells that are so bad they are going to die anyway. I have tested storing cells at 0% for 1.5 years, the voltage after storage has bounced back to higher than it was when starting the storage. They just don't self-discharge at all. I still won't recommend storing at 0% just because that is not usually done and there might be some reason I'm not aware about; just sayin' in my limited testing I haven't seen any ill effects storing at 0%.

Buying cells to build pack, I have noticed that Samsung had changed their factory charge level (at which cells are shipped) from 50% to about 30%, somewhere in 2018 or so. I don't know if this is to increase safety during shipping, or to increase the shelf life (which at 50% was already great), or maybe there is no special reason to do so. Just saying that the standard shipping charge level is between 30%-50%.

Anything between 3.5V to 3.9V is quite acceptable for long-term storage but between 3.5V and 3.7V would be even better.

Self-discharge in itself isn't problematic, irreversible damage is. But the two go hand-in-hand, in high state-of-charge and/or temperatures you have both elevated self-discharge and elevated capacity loss rate.

Below about 60% SoC at room temperatures or lower the self-discharge in good quality cells can be so low it's completely negligible and you can say they have no self-discharge. In my measurements, all measurements in such conditions were lost in noise, i.e., I would have needed way longer period of time than just 1.5 years, maybe 10 years to see how fast they actually lose charge.
« Last Edit: June 18, 2021, 11:53:14 am by Siwastaja »
 

Offline tiago1986

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Re: Battery Li-Po storage mode
« Reply #12 on: June 18, 2021, 11:59:46 am »
Yes self-discharge is slower at 3.6V than at 3.85V, but it's already very slow at 3.85V, at least compared to 4.20V.

You don't need to leave margin "in order not to self-discharge into death", that's a myth which only applies to cells that are so bad they are going to die anyway. I have tested storing cells at 0% for 1.5 years, the voltage after storage has bounced back to higher than it was when starting the storage. They just don't self-discharge at all. I still won't recommend storing at 0% just because that is not usually done and there might be some reason I'm not aware about; just sayin' in my limited testing I haven't seen any ill effects storing at 0%.

Buying cells to build pack, I have noticed that Samsung had changed their factory charge level (at which cells are shipped) from 50% to about 30%, somewhere in 2018 or so. I don't know if this is to increase safety during shipping, or to increase the shelf life (which at 50% was already great), or maybe there is no special reason to do so. Just saying that the standard shipping charge level is between 30%-50%.

Anything between 3.5V to 3.9V is quite acceptable for long-term storage but between 3.5V and 3.7V would be even better.

Self-discharge in itself isn't problematic, irreversible damage is. But the two go hand-in-hand, in high state-of-charge and/or temperatures you have both elevated self-discharge and elevated capacity loss rate.

Below about 60% SoC at room temperatures or lower the self-discharge in good quality cells can be so low it's completely negligible and you can say they have no self-discharge. In my measurements, all measurements in such conditions were lost in noise, i.e., I would have needed way longer period of time than just 1.5 years, maybe 10 years to see how fast they actually lose charge.
irreversible damage to LI-PO battery happens in which situation? i kept the lipo batteries near or at 100% for a few months and did it cause irreversible damage?


the temperature in my home ranges from 31-34°C for maximum long term storage is it better to keep Lipo at 3.85V or lower it to 3.6V??
 

Online Siwastaja

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Re: Battery Li-Po storage mode
« Reply #13 on: June 18, 2021, 12:03:27 pm »
Irreversible damage always happens, these products are not eternal. It's like food, it goes bad eventually.

A few months at 100% at your elevated temperature, you lose maybe 1% of the capacity. It isn't too bad.
 


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