# Looking for maintenance and care advice for Lithium ion battery pack



## ifoxbox (Feb 19, 2017)

I recently got a phantom drone for Christmas, and was wondering if the same rules for care and maintenance apply for a battery pack as it does for single cells? The specs of the battery are below:





Voltage of 15.2 Volts (4) 3.8v cells inside pack 
Max Charging Power – 100W 
Net Weight – 462 G 
Energy Level – 81.3 Wh 
Capacity of 5350 mAh. 
Operating Temperature of 14 degrees to 104 degrees Fahrenheit (-10 to 40 celsius) 
Battery Type – Lithium Ion Polymer LiPo 4S 

My main questions are:

Is it OK to drain down to 20% capacity left during each use? I've read that you should never go below 80% discharge for max overall battery life. Is that right, or should that number be lower?

I know for long term storage it is a good idea to store at 50%, but if I will be using them at least every week or two, would I be better off keeping them stored fully charged? 

Lastly, is it a good idea to do a full discharge every few months or so?

Thanks in advance for any advice you can give!


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## SilverFox (Feb 19, 2017)

Hello Ifoxbox,

I think the 20% left is a good target to shoot for.

Long term storage is usually longer than 1 week. If it is not too much trouble it is better to store at 50% and charge prior to use. If that is not convenient just charge them and use them.

No full discharge is necessary or recommended.

Tom


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## olemil (Feb 20, 2017)

LiPo packs like to be stored at 3.85v per cell.


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## ifoxbox (Feb 20, 2017)

SilverFox said:


> Hello Ifoxbox,
> 
> I think the 20% left is a good target to shoot for.
> 
> ...



Thanks Tom! I was hoping you would chime in. I always value your input! :thumbsup:

So after I drain the battery down to 20%, I should just charge it back up to 50% and then finish the charge the next week before I plan to use it again?





olemil said:


> LiPo packs like to be stored at 3.85v per cell.



Thanks for the info!


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## Gauss163 (Feb 20, 2017)

Based on numerous studies, the general rule of thumb for Li-ion batteries is: to maximize life, minimize the time that the battery spends at extreme voltages and high temperatures (which accelerate internal processes that cause degradation). For example, one of the worst things you could do is to keep your cells floating at 100% SOC on standby charge (or frequent top-ups), since this means that the cells will spend most of their life at the highest extreme voltage. Better to design a charging regimen that maximizes the time they spend near 50% capacity (e.g. store at 50% then top-up as close to use as is practical). See this later post for specific data from studies.


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## Gauss163 (Feb 20, 2017)

olemil said:


> LiPo packs like to be stored at 3.85v per cell.



That is too high SOC (70%) for storing some common chemistries. The optimal storage range is between 40-50% SOC. To determine the corresponding resting voltages see e.g. HKJ's page for a few common chemistries.


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## marinemaster (Feb 20, 2017)

I think a voltmeter would be in order but since you have a battery pack not sure how you would measure it and even if you can what would the optimal voltage be, since they are in series, as I understand. Hoping that each battery has the same discharge rate but if they don't and have say a 20% difference that is too much of a difference between the batteries in the pack. The 18650 I have I measure each one individually, the lights I have only take 1x18650.


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## novarider (Feb 21, 2017)

Gauss163 said:


> That is too high SOC (70%) for storing some common chemistries. The optimal storage range is between 40-50% SOC. To determine the corresponding resting voltages see e.g. HKJ's page for a few common chemistries.



Lipo charges have a storage setting which charges them to 3.85v and this is the widely accepted voltage for long term storage.


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## Gauss163 (Feb 21, 2017)

novarider said:


> Lipo charges have a storage setting which charges them to 3.85v and this is the widely accepted voltage for long term storage.


 
Look at datasheets, etc. and you will learn that cell manufacturer's recommend storing at between 40-50% SOC (and that's what they are typically shipped at). The voltages corresponding to 40-50% SOC *depend on the chemistry.
*
For many chemistries (esp. older ones) 3.85V is about 55% SOC, but for many newer chemistries it is much higher - about 70%, whereas 50% is about 3.65V. Hobby chargers cannot determine the chemistry so if they have a fixed storage voltage target value then that has to be a compromise value that suffices for most chemistries. e.g. they cannot choose 3.65V since that is only about 6% SOC for older chemistries. If you want optimal storage values you need a charger with programmable storage charging (or a general CC/CV charger).


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## olemil (Feb 21, 2017)

To the OP: You might want to have a look here, lots of valuable info on Lipo packs including safety tips. Also there are many threads on Multi-rotors so you can probably pick a few tips on your Phantom. Not sure where you are located but if you are in the US, you are supposed to register with the FAA to make it legal to fly.


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## olemil (Feb 21, 2017)

Gauss163 said:


> Look at datasheets, etc. and you will learn that cell manufacturer's recommend storing at between 40-50% SOC (and that's what they are typically shipped at). The voltages corresponding to 40-50% SOC *depend on the chemistry.
> *
> For many chemistries (esp. older ones) 3.85V is about 55% SOC, but for many newer chemistries it is much higher - about 70%, whereas 50% is about 3.65V. Hobby chargers cannot determine the chemistry so if they have a fixed storage voltage target value then that has to be a compromise value that suffices for most chemistries. e.g. they cannot choose 3.65V since that is only about 6% SOC for older chemistries. If you want optimal storage values you need a charger with programmable storage charging (or a general CC/CV charger).



Funny I have about $1000 worth of LiPo packs for my RC hobby. Every pack I have ever bought (NEW) shipped at a storage voltage of 3.85v/cell. Must be a lot of LiPo battery companies that don't know what the hell they are doing. All the hobby chargers I have owned over the years have an adjustable storage voltage setting ( for various battery chemistries ) including my current one, ICharger 308 DUO. PS, the default storage voltage for LiPo batteries is 3.85v/cell. 

* LiPo settings Taken from my 308 DUO manual:
*
Storage Cell Voltage:
_3.7V/Cell-3.9V/Cell; _
_Default: 3.85V/Cell 
_Storage Compensation: 
_0V/Cell-0.2V/Cell; _
_Default: 0.01V/Cell 
_


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## Gauss163 (Feb 21, 2017)

olemil said:


> Funny I have about $1000 worth of LiPo packs for my RC hobby. Every pack I have ever bought (NEW) shipped at a storage voltage of 3.85v/cell. [...]



Again, optimal storage voltage *depends on the particular Li-ion chemistry* of the cells. Probably your LiPo pack recommendations are based on the fact that most of the chemistries used in the RC/hobby packs were/are close to 50% SOC around 3.85V. But that is not true for many other common modern Li-ion chemistries, where 50% SOC is about 3.65V. For example, this is true for all of the 18650 cells except the first two in _HKJ's SOC vs Voltage page_. This includes many common cells used in flashlights, vaping, powerbanks, laptops, etc (Panasonic CGRs and NCRs)

For example, below is a table from said page. Notice that the first two columns shows chemistries like your LiPo, where 50% SOC occurs between 3.8-3.9V, but the final three columns shows cells where 50% SOC occurs between 3.6-3.7V.


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## PapaLumen (Feb 21, 2017)

Which Phantom do you have? White DJI battery? My Phantom 2 flashes red lights and lands itself when down to about 20%. And yes charging back to about 50% and fully charging the night before use would be the best way to store them. No benefit in running them down every few months etc.


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## olemil (Feb 21, 2017)

Gauss163 said:


> Again, optimal storage voltage *depends on the particular Li-ion chemistry* of the cells. Probably your LiPo pack recommendations are based on the fact that most of the chemistries used in the RC/hobby packs were/are close to 50% SOC around 3.85V. But that is not true for many other common modern Li-ion chemistries, where 50% SOC is about 3.65V. For example, this is true for all of the 18650 cells except the first two in _HKJ's SOC vs Voltage page_. This includes many common cells used in flashlights, vaping, powerbanks, laptops, etc (Panasonic CGRs and NCRs)


Ok


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## ifoxbox (Feb 21, 2017)

PapaLumen said:


> Which Phantom do you have? White DJI battery? My Phantom 2 flashes red lights and lands itself when down to about 20%. And yes charging back to about 50% and fully charging the night before use would be the best way to store them. No benefit in running them down every few months etc.



Yes, it is the white DJI battery. Mine has an option to choose when to give the low battery warning. I have it set to 30%, and monitor it from there to be sure I land at 20%. I will charge back up to 50% later that day and then do a full charge before the next use.

Thanks everyone for all the help!


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## novarider (Feb 22, 2017)

Gauss163 said:


> Again, optimal storage voltage *depends on the particular Li-ion chemistry* of the cells. Probably your LiPo pack recommendations are based on the fact that most of the chemistries used in the RC/hobby packs were/are close to 50% SOC around 3.85V. But that is not true for many other common modern Li-ion chemistries, where 50% SOC is about 3.65V. For example, this is true for all of the 18650 cells except the first two in _HKJ's SOC vs Voltage page_. This includes many common cells used in flashlights, vaping, powerbanks, laptops, etc (Panasonic CGRs and NCRs)
> 
> For example, below is a table from said page. Notice that the first two columns shows chemistries like your LiPo, where 50% SOC occurs between 3.8-3.9V, but the final three columns shows cells where 50% SOC occurs between 3.6-3.7V.



Your trying to prove your right on a subject he didn't even ask about. He's asking about his lipo pack not 18650 batteries. 

There are millions of lipo packs sold and they all are shipped at 3.85v. The recommended storage charge is 3.85v.


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## olemil (Feb 22, 2017)

novarider said:


> Your trying to prove your right on a subject he didn't even ask about. He's asking about his lipo pack not 18650 batteries.
> 
> There are millions of lipo packs sold and they all are shipped at 3.85v. The recommended storage charge is 3.85v.



Thank you. :thumbsup:


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## Gauss163 (Feb 23, 2017)

novarider said:


> Your trying to prove your right on a subject he didn't even ask about. He's asking about his lipo pack not 18650 batteries.
> There are millions of lipo packs sold and they all are shipped at 3.85v. The recommended storage charge is 3.85v.



Not true. I supplied the industry standard optimal storage targets, typically 35-50% SOC (depending on storage time, ambient temperature).

Be aware that a lot of info in the RC/hobby world is outdated, e.g. many RC chargers use cloned firmware that still has the _ancient _distinction between Li-ion(3.6/4.1) vs LiPo(3.7/4.2). 

Even for higher voltages chemistries typically used in RC packs (where 3.85V is about 55% S0C), this is not the storage SOC that is _optimal_ for prolonging life. Rather, optimal storage SOC is typically between 35-50% SOC (about 3.77-3.82V). For example, if you look at the datasheet for Sanyo/Panasonic NCR18650BE you will see that they are shipped at 35% SOC, i.e. slightly over one-third capacity.


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## olemil (Feb 23, 2017)

ifoxbox, please do yourself a favor and go to the site I posted in post #10, there is a vast amount of hands on knowledge there on LiPo packs. LiPo packs are not something to misuse, if you don't believe me do a search on YouTube for LiPo fires. Hope you are enjoying your Phantom, I have a DJI F450 and love it.


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## Gauss163 (Feb 23, 2017)

olemil said:


> I feel bad paying $280 for my charger now knowing it has outdated/ancient firmware......NOT!!!!!!! It's funny my charger has several types of battery chemistries to choose from for charging, discharging, storage charge and they all have different voltages depending which chemistry you choose.



Which has nothing to do with what I wrote. 

I've owned over 30 RC/hobby charger models, ranging from earliest models (Bantam, Victor, etc) to more recent models (iChargers, Hyperions, etc). In my opinion, there has been very little innovation since the early days (primarily because of rampant cloning). 

You won't learn much about battery electrochemistry from hobby charger manuals. The hobby charger engineers are electrical engineers - not experts in battery electrochemistry. If you want to learn about finer points of battery electrochemistry you should look elsewhere.


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## novarider (Feb 25, 2017)

Gauss163 said:


> Not true. I supplied the industry standard optimal storage targets, typically 35-50% SOC (depending on storage time, ambient temperature).
> 
> Be aware that a lot of info in the RC/hobby world is outdated, e.g. many RC chargers use cloned firmware that still has the _ancient _distinction between Li-ion(3.6/4.1) vs LiPo(3.7/4.2).
> 
> Even for higher voltages chemistries typically used in RC packs (where 3.85V is about 55% S0C), this is not the storage SOC that is _optimal_ for prolonging life. Rather, optimal storage SOC is typically between 35-50% SOC (about 3.77-3.82V). For example, if you look at the datasheet for Sanyo/Panasonic NCR18650BE you will see that they are shipped at 35% SOC, i.e. slightly over one-third capacity.



Yes it is true you just did it again. Ncr18650b batteries are not what he was asking about. What your saying is that EVERY SINGLE lipo manufacturer including the highest quality and most respected companies are all wrong and your right. simply because you saw a data sheet for 18650 batteries which is not even what we're discussing. 

Do some searching for info on lipo batteries NOT 18650 and you will see they recommend 3.85v for storage. This comes from the battery manufacturer. 

A quick Google search for lipo battery care and this is from the first link: For the longest life of the batteries, LiPos should be stored at room temperature at 3.8V per cell. 

Scroll down to the 3rd result and you get this 
Maxamps website says: Storage Procedure: When not using your LiPo/Life battery pack, store it at 60-70% of the pack’s rated capacity. 

There are many more if you care to look.


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## Tachead (Feb 25, 2017)

novarider said:


> Lipo charges have a storage setting which charges them to 3.85v and this is the widely accepted voltage for long term storage.




+1


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## Tachead (Feb 25, 2017)

Gauss163 said:


> Look at datasheets, etc. and you will learn that cell manufacturer's recommend storing at between 40-50% SOC (and that's what they are typically shipped at). The voltages corresponding to 40-50% SOC *depend on the chemistry.
> *
> For many chemistries (esp. older ones) 3.85V is about 55% SOC, but for many newer chemistries it is much higher - about 70%, whereas 50% is about 3.65V. Hobby chargers cannot determine the chemistry so if they have a fixed storage voltage target value then that has to be a compromise value that suffices for most chemistries. e.g. they cannot choose 3.65V since that is only about 6% SOC for older chemistries. If you want optimal storage values you need a charger with programmable storage charging (or a general CC/CV charger).



He is asking about Lithium Polymer Gauss, not other chemistries:shakehead. 3.85V is what most, if not all, lipo manufactures recommend for storage.


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## Tachead (Feb 25, 2017)

novarider said:


> Yes it is true you just did it again. Ncr18650b batteries are not what he was asking about. What your saying is that EVERY SINGLE lipo manufacturer including the highest quality and most respected companies are all wrong and your right. simply because you saw a data sheet for 18650 batteries which is not even what we're discussing.
> 
> Do some searching for info on lipo batteries NOT 18650 and you will see they recommend 3.85v for storage. This comes from the battery manufacturer.
> 
> ...



+1, good post with accurate information.

Gauss is a known trouble maker. He has been reprimanded and banned several times but, still causes trouble. I suggest you don't waste your time arguing with him:thumbsup:


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## Tachead (Feb 25, 2017)

ifoxbox said:


> I recently got a phantom drone for Christmas, and was wondering if the same rules for care and maintenance apply for a battery pack as it does for single cells? The specs of the battery are below:
> 
> 
> 
> ...



I recommend checking your packs resting voltage after you fly. You only want to drain your lipos to 3.7-3.75V per cell if you want the best life and performance out of them. Store them at 3.85V if you plan on not using them for more then a day or two. Most hobby chargers have a storage mode to do this automatically for you.

Get yourself a simple tester like this one...

http://media.hyperion.hk/dn/sentry/

It will show you the voltage of each cell in your packs by plugging in the balance connector. That way you can monitor both the voltage and how well your charger is balancing the individual cells. A tester like this and a high quality charger is a must for every RC hobbyist imo.


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## olemil (Feb 25, 2017)

Tachead said:


> I recommend checking your packs resting voltage after you fly. You only want to drain your lipos to 3.7-3.75V per cell if you want the best life and performance out of them. Store them at 3.85V if you plan on not using them for more then a day or two. Most hobby chargers have a storage mode to do this automatically for you.
> 
> Get yourself a simple tester like this one...
> 
> ...



Great advice, thank you. :thumbsup: I've had my EOS Sentry for years and love it, a must have for the money to monitor your packs easily.


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## Tachead (Feb 25, 2017)

olemil said:


> Great advice, thank you. :thumbsup: I've had my EOS Sentry for years and love it, a must have for the money to monitor your packs easily.




No problem:thumbsup:. RC helicopters are one of my other hobbies and I have had my EOS Sentry and another tester for years as well. A high quality charger and a good tester are definitely essential to properly maintain your lipos and keep safe in the RC hobby. Lipo batteries can be very dangerous and even more care should be taken then with normal cylindrical lithium ions like 18650's.


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## Gauss163 (Feb 25, 2017)

@Tachead Yet more unfounded ad hominem attacks are not the proper way to dispute scientific claims. As always, if anyone has any questions about any claims then please feel welcome to ask and I will provide further data to back up those claims (beyond HKJ's voltage vs SOC graphs above).

A couple more points deserve mention regarding shipping/storage SOC. One of the reasons that rewrappers and other Li-ion battery resellers employ a very conservative shipping/storage charge around 55% SOC is due to the fact that these packs/cells may sit on the shelf in (possibly hot) warehouses for quite some time, so they use a more conservative (higher) shipping voltage charge to make sure they do no drain too low even if they do not sell for some time. It also makes sense to recommend more conservative storage values to users, so that they don't have to deal with warranty claims and/or complaints from users who forgot to recharge their batteries after leaving them in storage for too long (which often occurs). 

Note that the self-discharge rate depends on many factors, temperature, chemistry, BMS quiescent current , etc. Generic storage SOC recommendations (e.g. in a charger manual) have to account for all these variations, so are typically less optimal than recommendations that are specialized to specific chemistry and BMS, etc.

Finally, it goes without saying that battery sellers make more money when batteries have shorter life, so they don't have a strong incentive to provide information that yields maximal lifetime. For example, Dell laptops once had a built-in timer that would wrongly claim that the batteries needed replacing - which led to a lawsuit; further they did not supply battery saver software until forced to do so by competition. Accessories like batteries are a huge source of profit for battery-powered devices, so manufacturers typically do the least possible when it comes to educating consumers about how to optimize calendar or cycle life.


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## olemil (Feb 25, 2017)

Tachead said:


> No problem:thumbsup:. RC helicopters are one of my other hobbies and I have had my EOS Sentry and another tester for years as well. A high quality charger and a good tester are definitely essential to properly maintain your lipos and keep safe in the RC hobby. Lipo batteries can be very dangerous and even more care should be taken then with normal cylindrical lithium ions like 18650's.



Nice to see a fellow RC heli enthusiast on here. Yes LiPo fires are very scary to say the least!! I store mine in vented ammo cans which are stored in a large metal cabinet. Sorry to drift off topic.


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## Tachead (Feb 25, 2017)

Gauss163 said:


> @Tachead Yet more unfounded ad hominem attacks are not the proper way to dispute scientific claims. As always, if anyone has any questions about any claims then please feel welcome to ask and I will provide further data to back up those claims (beyond HKJ's voltage vs SOC graphs above).
> 
> A couple more points deserve mention regarding shipping/storage SOC. One of the reasons that rewrappers and other Li-ion battery resellers employ a shipping charge a bit higher than 50% SOC is due to the fact that these packs/cells may sit on the shelf in (possibly hot) warehouses for quite some time, so they use a more conservative (higher) shipping voltage charge to make sure they do no drain too low even if they do not sell for some time. It also makes sense to recommend more conservative storage values to users, so that they don't have to deal with warranty claims and/or complaints from users who forgot to recharge their batteries after leaving them in storage for too long (which often occurs).
> 
> ...



Gauss, as said, we are not talking about cylindrical lithium ions in this thread. We are talking about lithium polymer hobby packs. Therefore, HKJ's chart you posted does not apply here and is off topic. Most lithium polymer hobby pack manufacturers recommend 3.85V be used for storage. Most high end hobby chargers(not clones) also use this voltage for their storage modes. Your posts are off topic in this thread, are riddled with misinformation on this topic(Lipo hobby packs), and your disrupting yet another thread in the battery forum. Please stop posting about off topic subjects and derailing this thread.


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## Gauss163 (Feb 25, 2017)

Tachead said:


> Gauss, as said, we are not talking about cylindrical lithium ions in this thread. We are talking about lithium polymer hobby packs [...]



Which is not relevant, because the storage voltage does not depend on the enclosure but, rather, on chemistry and other factors that I enumerated above.


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## Tachead (Feb 25, 2017)

olemil said:


> Nice to see a fellow RC heli enthusiast on here. Yes LiPo fires are very scary to say the least!! I store mine in vented ammo cans which are stored in a large metal cabinet. Sorry to drift off topic.



Sure is nice to see some other RC enthusiasts. You are not off topic. The OP should know the dangers of lipos and the precautions that should be taken to stay safe and keep them healthy. Hope this info helps you ifoxbox:thumbsup:


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## Overclocker (Feb 25, 2017)

i agree w/ gauss163 here. "lipo" is just a generic term for pouch cells. there are TONS of different formulations out there yielding different curves. the 3.85v "storage" setting on hobby chargers is just a rule of thumb. it isn't necessarily the optimal storage voltage for all flavors of lipo

but then again it's just a small pack so don't worry about it too much. when you start having larger packs then it starts to make sense to try to maximize its life. perhaps the biggest factor is temperature, so keep them cool.


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## Tachead (Feb 25, 2017)

Gauss163 said:


> Which is not relevant, because the storage voltage does not depend on the enclosure but, rather, on chemistry and other factors that I enumerated above.



The Lipo packs the OP is talking about are not the same as 18650's Gauss. Modern lithium polymer and graphene lithium polymer packs can handle up to 95C discharge rates. Some of the best high drain 18650's on the market like the Sony VTC6 can only handle like 5-10C. The manufacturers of these cells recommend 3.7-3.9V for storage so, that is what they should be stored at. These Lipo packs also shouldn't be discharged as low as common 18650's. The minimum recommended resting discharge voltage for many lipo batteries is 3.3V vs. 2.5V for most 18650's. 

As always, the manufacturer of a particular cell or pack lists recommendations for charging, storage, usage, etc. for their products and these recommendations are the ones that should be studied and followed. Not the recommendations some guys on a forum because as you can see opinions, beliefs, and knowledge can vary.


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## Tachead (Feb 25, 2017)

Overclocker said:


> i agree w/ gauss163 here. "lipo" is just a generic term for pouch cells. there are TONS of different formulations out there yielding different curves. the 3.85v "storage" setting on hobby chargers is just a rule of thumb. it isn't necessarily the optimal storage voltage for all flavors of lipo
> 
> but then again it's just a small pack so don't worry about it too much. when you start having larger packs then it starts to make sense to try to maximize its life. perhaps the biggest factor is temperature, so keep them cool.



Most lipo manufactures recommend a 3.7-3.9V storage voltage. 3.85V is right in the middle of this recommendation with a little extra added to allow for self discharge during extended storage. This is probably why most high end charger companies chose this voltage for their storage modes. Is this voltage the exact best storage voltage for all chemistries and ambient temperatures? No but, it is a pretty good rule of thumb and there is no point in splitting hairs here imo. 

I wouldn't exactly call a 5350mAh 4S $235 lipo a small pack:thinking:. That's a pretty significant expense even compared to one of our 4 x 18650 lights using the best cells.


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## Gauss163 (Feb 25, 2017)

Tachead said:


> Most lipo manufactures recommend a 3.7-3.9V storage voltage. [...]



RC/hobby pack manufacturers (unlike the big guys Panasonic, Sony, LG etc) do not have large research labs that can do accelerated degradation testing etc. The recommendations they supply are very conservative generic ballpark figures that they have been supplying since the early days. But many improvements have been made since then (e.g. lowering self-discharge rates). The optimal storage values are often far from those generic values (but the specifics depend on many parameters). If you know what you are doing you can attain significant longetivity gains by using more optimal values.


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## Tachead (Feb 25, 2017)

Gauss163 said:


> RC/hobby pack manufacturers (unlike the big guys Panasonic, Sony, LG etc) do not have large research labs that can do accelerated degradation testing etc. The recommendations they supply are very conservative generic ballpark figures that they have been supplying since the early days. But many improvements have been made since then (e.g. lowering self-discharge rates). The optimal storage values are often far from those generic values (but the specifics depend on many parameters). If you know what you are doing you can attain significant longetivity gains by using more optimal values.



I'm sorry Gauss but you are talking out your butt now. You have no idea what lipo manufacturers have for research labs or what equipment they use. You also have no idea how accurate or dated the recommendations they supply are. Lithium polymer cells are used in a lot more then just the RC industry and are the main cell used in most cell phones, tablets, and laptops these days. They are far from old tech and are constantly being researched and improved just like cylindrical cells. In fact some of the newest battery technology(graphene enhanced lithium ion) has been readily available in lithium polymer RC packs for a while now but, is yet to be incorporated in any commercially available cylindrical products(18650's) that I am aware of. 

There is no need to overthink this or split hairs OP. Storing Lithium polymer packs anywhere between 3.7 and 3.9V, like their manufactures recommend, is fine and I would trust them over Gauss. The 3.85V storage mode on most chargers is a reasonable and well thought out value imo considering all the different conditions, storage times, and chemistries that an average user might encounter. Gauss can calculate right down to the 0.001V what is the ideal storage voltage for his particular cell and ambient temperature if he wants and he will likely see little benefit. Us normal folk have better things to do imo.


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## Gauss163 (Feb 25, 2017)

Tachead said:


> I'm sorry Gauss but you are talking out your butt now. You have no idea what lipo manufacturers have for research labs or what equipment they use. You also have no idea how accurate or dated the recommendations they supply are [...]



It's your prerogative to believe whatever you desire. My knowledge on these topics was garnered from a couple decades professional experience working in this industry, including many conversations with engineers from top-tier manufacturers (including Panasonic, Sanyo and LG). That's not "talking out of your butt". Rather, it is passing along intuition gained from leading experts in the industry.


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## Overclocker (Feb 26, 2017)

Tachead said:


> I wouldn't exactly call a 5350mAh 4S $235 lipo a small pack:thinking:. That's a pretty significant expense even compared to one of our 4 x 18650 lights using the best cells.




well to me that's small haha. right now i'm building a 204-cell pack. 17-series 12-parallel for an electric lightweight motorcycle. i just keep the cells NEAR their optimal "storage" voltage. no need to be anal about keeping them within 1 millivolt

the OP might want to refrigerate his packs. based on what i read the temperature is a bigger factor than voltage. that's why electric car packs have chillers


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## novarider (Feb 28, 2017)

Gauss163 said:


> RC/hobby pack manufacturers (unlike the big guys Panasonic, Sony, LG etc) do not have large research labs that can do accelerated degradation testing etc. The recommendations they supply are very conservative generic ballpark figures that they have been supplying since the early days. But many improvements have been made since then (e.g. lowering self-discharge rates). The optimal storage values are often far from those generic values (but the specifics depend on many parameters). If you know what you are doing you can attain significant longetivity gains by using more optimal values.



If your going to tell people lipo battery manufacturers are wrong at least be able to back it up. Do some googling and post here what you find. Again lipo batteries not 18650. 

"someone once told me" is not proof


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## Gauss163 (Feb 28, 2017)

novarider said:


> If your going to tell people lipo battery manufacturers are wrong at least be able to back it up. Do some googling and post here what you find. Again lipo batteries not 18650.
> 
> "someone once told me" is not proof


 
No one claimed that the generic storage targets are "wrong". Rather, they are nonoptiimal, and the reasons for that have been enumerated above (and have nothing to do with "someone once told me").


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## magellan (Feb 28, 2017)

their manufactures recommend, is fine and I would trust them over Gauss. The 3.85V storage mode on most chargers is a reasonable and well thought out value imo considering all the different conditions, storage times, and chemistries that an average user might encounter. Gauss can calculate right down to the 0.001V what is the ideal storage voltage for his particular cell and ambient temperature if he wants and he will likely see little benefit. Us normal folk have better things to do imo.[/QUOTE]

Yeah, sometimes I like to ignore the accepted science and engineering myself just to see if it blows up in my face. Otherwise you'll never have anything interesting to talk about in the locker room.


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## Tachead (Feb 28, 2017)

Gauss163 said:


> No one claimed that the generic storage targets are "wrong". Rather, they are nonoptiimal, and the reasons for that have been enumerated above (and have nothing to do with "someone once told me").



Gauss, some people leave their packs and/or 18650's at full charge all year round and still get many years and hundreds of cycles out of them at a respectable capacity. You are making it sound like if you don't keep your cells at the exact "optimum" storage level they will quickly die or explode lol. The actual difference in capacity loss/cycle life between keeping a cell at the exact "optimal" storage to the millivolt, for the chemistry and ambient temperature, or being 0.1-0.2V higher or lower is probably so small that only a person with OCD or no life would even begin to care. 

And, I agree with the above poster. Your story of supposedly schmoozing with industry battery experts in Japan and South Korea holds no weight. Anyone can claim anything on the internet and your history around here doesn't exactly inspire confidence. Not too mention, the battery guys from Panasonic, Sony, and LG wouldn't exactly be experts on what other major cell manufacturers(many in other countries) have in their research and testing labs nor would they have unbiased opinions.

The other issue Gauss is you really have no idea how the chemistries of a particular lipo pack compare to the 18650's you are using as your guide. So, basing your charging practices on another cells data, when it could be completely different(and likely is), instead of the using the particular cells manufactures recommendations seams rather foolhardy if you ask me.


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## magellan (Feb 28, 2017)

[And, I agree with the above poster.]

Actually, I agree with what Gauss has posted. 

I was just saying that sometimes I do risky things.


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## Tachead (Feb 28, 2017)

magellan said:


> [And, I agree with the above poster.]
> 
> Actually, I agree with what Gauss has posted.
> 
> I was just saying that sometimes I do risky things.



You posted while I was typing that post. I was talking about novarider's post(#40).

You agree that you should use the charging recommendations from a totally different type of cell from a different cell manufacturer over what the actual cells manufacturer recommends?:thinking:. Do you use the manual from a Chevy Volt to learn how to use your Ford F250 Powerstroke too?


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## magellan (Feb 28, 2017)

[You posted while I was typing that post. I was talking about novarider's post(#40).]


Ok.

And as I'm presently on a ship off the coast of Borneo my screen refreshes do take a while due to the limited bandwidth.


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## Tachead (Feb 28, 2017)

magellan said:


> [You posted while I was typing that post. I was talking about novarider's post(#40).]
> 
> 
> Ok.
> ...



Nice, business or pleasure? If you have a light with you that could be a good entry for the pictures of lights around the world thread.


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## Gauss163 (Feb 28, 2017)

Tachead said:


> Gauss, some people leave their packs and/or 18650's at full charge all year round and still get many years and hundreds of cycles out of them at a respectable capacity.



Highly doubtful. Keeping packs at high voltages _greatly _accelerates internal degradation processes.



Tachead said:


> You are making it sound like if you don't keep your cells at the exact "optimum" storage level they will quickly die or explode lol [...]



Where did you get that strange idea? Claiming that storage voltages are nonoptimal implies nothing of the sort. Ditto for the rest of the (deleted) nonsense following that.



Tachead said:


> The other issue Gauss is you really have no idea how the chemistries of a particular lipo pack compare to the 18650's you are using as your guide [...]



The electrochemical processes that govern the major Li-ion battery degradation mechanisms are essentially uniform across all Li-ion chemistries. So your argument makes no sense (yet again).


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## magellan (Feb 28, 2017)

Tachead said:


> Nice, business or pleasure? If you have a light with you that could be a good entry for the pictures of lights around the world thread.



Mostly pleasure, although I used a lot of the time in the evening to write a technical article I've been thinking about for a while that turned out better than I was expecting.

But getting back to the battery issues, it sounds to me like you both have a lot of knowledge about the subject. Gauss is saying many of the same things I've read here by other knowledgeable people as well as in the technical literature. I've also seen others report the same experiences in practice that you've had. Who is right? Well, I guess that depends on your point of view.

For example, a big manufacturer of batteries with global sales in the tens or hundreds of millions will obviously need to have more conservative standards and recommendations just to cover their butts and because they have deep pockets. And presumably they know their own batteries pretty well. On the other hand, a very experienced user, who knows his batteries and equipment may feel that he can push the envelope a bit without too much risk. I sometimes do the same. Just my two cents, but this seems to me to be at the crux of your disagreement. Others mileage may vary.


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## Overclocker (Mar 1, 2017)

Gauss163 said:


> Highly doubtful. Keeping packs at high voltages _greatly _accelerates internal degradation processes.
> 
> 
> The electrochemical processes that govern the major Li-ion battery degradation mechanisms are essentially uniform across all Li-ion chemistries. So your argument makes no sense (yet again).





it's funny how people mistakenly think that lipos are fundamentally different from 18650. they seem to think that lipo means lithium polymer, as being different from "lithium ion". but actually it's "lithium ion polymer". i think that's where the confusion comes from.

there was a time when you couldn't change the charge limits on laptops so they ran hot all the time at 100%. cells didn't last long. here are my settings on my ThinkPad


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## Gauss163 (Mar 1, 2017)

Overclocker said:


> it's funny how people mistakenly think that lipos are fundamentally different from 18650. they seem to think that lipo means lithium polymer, as being different from "lithium ion". but actually it's "lithium ion polymer". i think that's where the confusion comes from.



Part of that confusion is due to the fact that the name LiPo or lithium polymer was originally used for cells that employed polymer (vs. liquid) _electrolyte_, whereas nowadays it generally refers to pouch cells (with polymer _casing_) but liquid electrolyte (same as in 18650 cells).

But also much confusion is due to rampant misinformation on the web. This is somewhat unique and due primarily to the fact that much of the information is considered proprietary by the manufacturers so not available to the general public. This vacuum was filled by guesses, old wives tales, marketing hype, pseudoscience, etc. It is a very difficult process to correct some of these mistakes when the misinformation has propagated so widely (e.g. to sites like Battery "University" - kudos to Wikipedia for blacklisting it).


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## novarider (Mar 2, 2017)

If they are exactly the same why can lipo batteries be charged at 5c(20A+) or higher safely while 18650 can only be charged at 1.5-2A safely? Lipo batteries also have much higher discharge rates than 18650 batteries.


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## Gauss163 (Mar 2, 2017)

@novarider They are not "exactly the same", but the differences do not alter electrochemcal properties that primarily govern storage degradation targets.


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## Tachead (Mar 2, 2017)

Gauss163 said:


> Highly doubtful. Keeping packs at high voltages _greatly _accelerates internal degradation processes.
> 
> 
> 
> ...



It's proven Gauss. Many people on here leave their spare cells fully charged all the time so they are ready to use and still get several years of service out of them. Would they have gotten more if they always kept them at storage? Sure but, the difference isn't as drastic as you make it out to be. And, the difference between storing them at their ideal storage voltage(for chemistry and ambient temp) vs. 0.1-0.2V higher or lower is likely hardly even noticeable to the average user. As an example, I have a 4 year old li-ion that has been cycled hundreds of times and was left at 100% charge 8-12 hours per day every day of those 4 years. That's between 11680 and 17520 hours or around 2 years at full charge. It doesn't have the same capacity it once did(nor would any cell this old and cycled this much) but, it still works well and has plenty of capacity.

You don't even know they are "nonoptimal" and have been using data for different cells from different manufacturers to base your claims on. And, then you go on to say that we should disregard the manufacturers charging data because it is outdated and inaccurate when you have no idea or proof if that is even true. You also have no proof that Panasonic, Sony, or LG has any better testing equipment or procedures then any of these lipo manufacturers yet you claim it anyway. You make it sound like these hobby pack lipo manufacturers are just some tiny warehouse in China. One of the companies that makes many of these hobby packs is one of the top battery companies in the world, does over 150 million in battery sales annually, and has over 3000 employees. Remember, they just make batteries too unlike Panasonic, Sony, or LG. 

Gauss, you have been claiming that the "optimal" storage voltage is "dependent on chemistry" all along. You even posted some charts to prove it. Now you're saying they are all the same? How does my argument not make sense? The charging data for other cells(18650's in this case) is irrelevant. The only data that matters is the data for the particular cell we are talking about because only the manufacture knows its particular cells chemistry and the best charging procedures for it. But, you are telling us we shouldn't follow the manufactures data because you(Mr expert) think it's flawed. I am sorry but, I am going to believe the manufacturer over some guy on the internet(you) who thinks they are an expert because they have read a few of HKJ's articles and can use google:shakehead.


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## Gauss163 (Mar 2, 2017)

Tachead said:


> It's proven Gauss. Many people on here leave their spare cells fully charged all the time so they are ready to use and still get several years of service out of them. [...]



Which proves absolutely nothing about _optimal _storage voltages. 

It is ridiculous how much misinformation has propagated in the RC/hobby charger world. Here's one way much misinformation has been propagated: Battery "University" picks up old-wives tales off of hobby forums and publishes them as if they were scientifically-proven facts. These dubious claims are then recycled by Chinese pack manufacturers who have little-to-no research budget so no capability to vet such claims. Some of the lower-tier hobby pack manufacturers actually explicitly refer to Battery University (as if it had some credibility). 

Needless to say you'd never find such nonsense from top-tier manufacturers. Caveat Emptor. Look elsewhere for accurate information.


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## Tachead (Mar 2, 2017)

Gauss163 said:


> Which proves absolutely nothing about _optimal _storage voltages.
> 
> It is ridiculous how much misinformation has propagated in the RC/hobby charger world. Here's one way much misinformation has been propagated: Battery "University" picks up old-wives tales off of hobby forums and publishes them as if they were scientifically-proven facts. These dubious claims are then recycled by Chinese pack manufacturers who have little-to-no research budget so no capability to vet such claims. Some of the lower-tier hobby pack manufacturers actually explicitly refer to Battery University (as if it had some credibility).
> 
> Needless to say you'd never find such nonsense from top-tier manufacturers. Caveat Emptor. Look elsewhere for accurate information.



You said it was "highly doubtful" I am just showing you that it is in fact quite probable and has been proven many times over by myself and other users. Furthermore, it proves that modern Li-ion/Lipo cells are very resilient and making sure that your cells are at the exact "optimal" storage voltage for all conditions at all times doesn't make a big difference for the average user. Even when abused they still offer a pretty amazing service life.

I like how you always disregard half of my posts lol. 

I agree that battery university is not a good place to source your knowledge, neither is wiki, nor from a flashlight forum user who thinks he knows it all and suggests using the data from totally different cells. It is much safer to go by the manufacturers recommendations imo. All good manufacturers include charging and storage recommendations in the literature that comes with their packs or on the packs themselves. If not, it can be found on their websites or datasheets. I'm looking at one of my hobby packs right now. It says right on the back "Store long term at 3.8V per cell." along with a bunch of other charging and usage info. Why would I ignore that and use the recommendations for a totally different cell from a different manufacturer:thinking:.

We are not talking about "low tier" hobby pack manufacturers here though nor 18650's. We are talking about a $235 DJI OEM lipo. Most hobby pack manufacturers don't even make the cells, they just assemble the packs and throw a label on them. And, RC enthusiasts don't use "low tier" packs for the most part either in my experience. I personally would never risk strapping an off brand "low tier" pack to one of my multi thousand dollar helis. Not only would it be too much risk but, it likely wouldn't offer the performance and longevity I require. 

Many hobby packs are made by top-tier cell manufacturers. My main supplier has over 200 engineers and technicians dedicated solely to research, development, and testing. I trust their charging recommendations and have had great performance and longevity by following them.


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## Gauss163 (Mar 2, 2017)

Tachead said:


> You said it was "highly doubtful" I am just showing you that it is in fact quite probable and has been proven many times over by myself and other users.



If you think that the anecdotes that you posted above constitute "proof many times over" then it's no wonder you don't understand what I wrote. Report back after you have hard data from carefully controlled tests so that we can determine precisely how much life you have lost by abusing your packs by storing them fully charged. 



Tachead said:


> It is much safer to go by the manufacturers recommendations imo.



Most hobby companies have little-to-nil expertise on such matters. They are simply passing along very rough, old rules of thumb that are far from optimal in many contexts.


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## nbp (Mar 2, 2017)

Oooook. This thread is becoming a debate between just two members. OBVIOUSLY, you are not going to convince each other. You've each said your part, let's leave it there and let some other folks carry on the discussion. Thank you in advance for your cooperation.


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## novarider (Mar 4, 2017)

Gauss has still not provided any proof whatsoever to his claims. Lipo batteries and 18650 batteries have very different discharge and charging capabilities and yet he still says they are the same. 


"Needless to say you'd never find such nonsense from top-tier manufacturers. Caveat Emptor. Look elsewhere for accurate information"

Please provide a link where a "top-tier" lipo manufacturer says to charge their batteries lower than 3.85v for storage


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## SilverFox (Mar 6, 2017)

There are some interesting ideas in this thread...

The driving question in my mind is at what discharge rate should the 50% state of charge be measured at...?

If my application is set up so I get hours of use from the battery pack, then I would review the data from Texas Instruments and the various cell manufacturers and go with their recommendations. On the other hand if my application only gives me minutes of use, my 50% level would involve higher voltages.

I recently purchased a jump pack. Its LiPo battery is advertised at a momentary maximum current of 4000 amps. Not bad for a 8 Ah battery pack.

I came across a diesel truck that had dead batteries. When I turned the key on, the dash wouldn't even respond. I hooked up the jump pack and discovered that the trucks batteries were at 1.8 volts. I hit the safety bypass on the jump pack and the voltage quickly rose to around 8 volts. I cranked a couple of times and finally the engine started. After disconnecting the jump pack and letting it cool down I checked and it was showing 75% left which corresponds to around 3.9 volts per cell from previous testing.

The next day I had to start the truck again. I hooked up the jump pack and noticed that the truck batteries were showing about 8 volts. I cranked the engine, but my pack ran out of power before the engine would start. I hit the low voltage shut off for the pack. After letting the pack cool down it was showing about 25% left in it. 

At roughly 600 amps, 50% state of charge is a little more than 3.9 volts per cell. Does that indicate that the "optimum" storage voltage for me is around 3.9 volts?

I never know when my jump pack will be needed and I want to make sure it does the job when it is needed. I also want to optimize its storage for longevity. My balance is to charge it to 4.0 volts per cell. This is less than full charge but still charged enough to get the job done when it is needed. The lesson I learned is that after using it I need to charge it back up prior to the next severe use.

This thread started with a discussion about optimized storage conditions for a drone's battery pack. If 50% state of charge is the metric I suppose you could run the drone for half of its run time, let the battery cool down and recover, then measure the batteries voltage. This would give you 50% state of charge for this application.

Theoretically, theory and practice should be close to the same. However in actual practice sometimes they are quite different. My round LiIon cells are around 7 - 8 years old. I have optimally stored them at 4.0 volts. They are still working very well...

Tom


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## Gauss163 (Mar 6, 2017)

SilverFox said:


> The driving question in my mind is at what discharge rate should the 50% state of charge be measured at...? [...]



Only in very extreme applications will that matter much, e.g. the jump-starter packs that you mentioned. I manage my jump-starter packs very differently from other Li-ion batteries.



SilverFox said:


> [...] My round LiIon cells are around 7 - 8 years old. I have optimally stored them at 4.0 volts. They are still working very well...



Why do you consider 4.0V to be optimal? 4.0V is about 80-85% SOC for common chemistries, which will likely cause more degradation than storing them in the recommended ranges of 35-50% SOC.


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## SilverFox (Mar 6, 2017)

Hello Gauss163,

Inquiring minds want to know...  

At what voltage do you store your jump packs at?

And,

Would drone and RC helicopter use be classified as extreme use?

I define "optimal" by combining cell degradation and intended use. My stored cells are ready to go in an emergency without needing to charge first, and 4.0 volts is easier on the cell than storing at 4.2 volts.

An argument could be made that in the best interest of the cells I may be better off investing in more cells and storing them at a lower state of charge. While I have pondered that my current regime seems to be working well so I most likely will continue.

I test my cells annually at 1C and compare the results to when the cells were new. I recycle my cells when their capacity drops below 80% of their initial capacity. 

Tom


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## Gauss163 (Mar 6, 2017)

SilverFox said:


> At what voltage do you store your jump packs at?



In the winter I store them at SOCs that will yield a few jump starts at lowest ambient temperatures.
In the summer I store them between 40-50% SOC.



SilverFox said:


> Would drone and RC helicopter use be classified as extreme use?



They differ in that jump-starters need to be on standby for use at unpredictable times, whereas drone use times are usually far more predictable (often scheduled), so one has the opportunity to exploit the known use times to develop much more optimal storage charging schemes, e.g. storing at optimal voltages, then topping up as close to use-time as proves convenient.


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## SilverFox (Mar 6, 2017)

Hello Gauss163,

If I have a drone that has 20 minutes of run time and fully charge it and then run it for 10 minutes, I should be at 50% state of charge. Even if the resting voltage of the pack is showing 3.85 volts per cell.

Correct?

Tom


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## Gauss163 (Mar 6, 2017)

SilverFox said:


> If I have a drone that has 20 minutes of run time and fully charge it and then run it for 10 minutes, I should be at 50% state of charge. Even if the resting voltage of the pack is showing 3.85 volts per cell. Correct?



The recommended storage voltage ranges are designed to minimize the degradation caused during the portion of calendar life spent in storage. These ranges are designed to not be so high that that the high voltage accelerates internal degradation processes, nor so low that the pack could self-discharge to low SOC levels that are also unhealthy.

Suppose we have a high-current device such that the pack capacity at the high-current rate is only half of the nominal (C/5) capacity. In your example, if you discharge it at the high-current rate to 50% of the high-rate capacity, then you are only discharging 25% of nominal capacity. So when the pack reaches resting voltage it will be at 75% SOC (typically 3.90-3.97V). That is far from the optimal recommended ranges. Jump-start packs are an even more extreme example of this difference between nominal and very-high-rate capacity.


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## novarider (Mar 7, 2017)

Gauss, I'm still waiting on a link to a "top-tier" lipo manufacturer that recommends storing their batteries as low as you say they should be.


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## Tachead (Mar 7, 2017)

SilverFox said:


> Hello Gauss163,
> 
> If I have a drone that has 20 minutes of run time and fully charge it and then run it for 10 minutes, I should be at 50% state of charge. Even if the resting voltage of the pack is showing 3.85 volts per cell.
> 
> ...



I recommend you store your drone's lipo packs at the recommended voltage provided by the manufacturer. It is usually written on the pack or available at the manufactures website. And yes, your method works well. Fully discharging your packs until low voltage cutoff may shorten their life and most hobbyists generally only like to discharge to about 3.7-3.75V. Most lipo pack manufactures recommend a storage voltage between 3.7 and 3.9V from my experience so the usual storage mode of 3.85V on most hobby chargers works well and is convenient if you miss the mark with your flight. I store my packs at the manufactures storage recommendations and have gotten years of service and many cycles out of them. So have the many other RC hobbyists I know and fly with. 

Gauss is no expert(unless you consider Googlefoo a skill that one can be considered an expert of), he just regurgitates information and charts gathered from Wiki, Battery University, and HKJ's site and likes to think he is more knowledgeable then engineers and experts from multi-million dollar battery manufacturers. The information he has provided in this thread is mainly for different types of cells from different manufactures. He has even stated that the information and recommendations from most lipo manufactures is erroneous but, offers no proof and seems to think his word holds more weight then the hundreds of engineers and experts that some of these companies employ. I wouldn't trust anything he says personally but, YMMV.


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## Gauss163 (Mar 7, 2017)

Tachead said:


> Gauss is no expert (unless you consider Googlefoo a skill that one can be considered an expert of), he just regurgitates information and charts gathered from Wiki, Battery University [...]



You know _absolutely nothing_ about my professional background, yet you continue to make completely unfounded personal attacks such as the above. Furthermore, what you wrote makes it quite clear that you aren't even bothering to pay close attention to what I write, since anyone who does knows quite well that I don't consider Battery University to be a reliable source. That speaks volumes about how completely unreliable your claims are. If you wish to dispute some claim then the proper way is not to make (unfounded) personal attacks on the author but, rather, to provide links to reputable (scientific) sources that support your views.

You cannot possibly gain deep knowledge about battery electrochemistry from rough generic guidelines in hobby charger manuals, battery pack labels, etc. Continuing to stubbornly interpret such as the bible on battery electrochemistry is not the path to enlightenment. Nor is behaving in puerile ways that will alienate knowledgeable users that attempt to share their professional expertise in hobby forums.


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## Tachead (Mar 7, 2017)

Gauss163 said:


> You know _absolutely nothing_ about my professional background, yet you continue to make completely unfounded personal attacks such as the above. Furthermore, what you wrote makes it quite clear that you aren't even bothering to pay close attention to what I write, since anyone who does knows quite well that I don't consider Battery University to be a reliable source. That speaks volumes about how completely unreliable your claims are. If you wish to dispute some claim then the proper way is not to make (unfounded) personal attacks on the author but, rather, to provide links to reputable (scientific) sources that support your views.
> 
> You cannot possibly gain deep knowledge about battery electrochemistry from rough generic guidelines in hobby charger manuals, battery pack labels, etc. Continuing to stubbornly interpret such as the bible on battery electrochemistry is not the path to enlightenment. Nor is behaving in puerile ways that will alienate knowledgeable users that attempt to share their professional expertise in hobby forums.



I may not but, the fact that all the information and charts you post come from Wiki, HKJ's site, etc. instead of scientific publications, text books, and research studies speaks volumes imo. I try not to pay close attention to what you write because me along with several others(as you can see from this thread alone) have realized you are just another know it all armchair cowboy with too much time on his hands that thinks he is an expert because he can use google. I don't have to support my views Gauss. I don't claim to be an expert like you and my view is simply that following the manufacturers recommendations instead of some know it all on the internet is a better and safer course of action. The only one who really knows how their cells should be cared for is the manufacturer because they are the ones that made the cells and are the only one who knows the actual specifications, chemistry, and engineering of their particular cells. 

I said nothing about "gaining deep knowledge of battery electrochemistry" nor that "hobby charger manuals and battery pack labels are the bible on electrochemistry". I simple said that a manufactures labels should be followed because they made the cells. There are thousands of different cell designs and variations of a particular cell chemistry(that is why cells even of the same general chemistry don't all perform the same) and the manufacturer is the only one who knows these specs. So, why you would suggest going against their recommendations is beyond me. It is careless and egotistical to make such recommendations and assume your knowledge is superior to the hundreds of engineers and technicians that R&D, produce, and test their cells.


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## nbp (Mar 7, 2017)

nbp said:


> Oooook. This thread is becoming a debate between just two members. OBVIOUSLY, you are not going to convince each other. You've each said your part, let's leave it there and let some other folks carry on the discussion. Thank you in advance for your cooperation.



Remember when I posted this? 

Stop trolling each other. Seriously.


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## Gauss163 (Mar 7, 2017)

For readers who are actually interested in the science behind these matters, below are some graphs from a recent study that show how degradation typically depends on storage SOC. This is for NCA chemistry, whose degradation properties are less severe then other common chemistries. Just as I described above, you can see how the internal resistance and capacity fade increases at higher storage SOC levels. 





Excerpted from: Comparison of Plug-In Hybrid Electric Vehicle Battery Life Across Geographies and Drive Cycles, by Kandler Smith et al., National Renewable Energy Laboratory, 2012.


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## SilverFox (Mar 7, 2017)

Hello Gauss163,

While I agree with what you are illustrating with you supposition, it is flawed.

You are illustrating what happens when you use a high capacity cell in a high current application. High capacity cells tend to have higher internal resistance and that cause them to heat up during high discharge rates. The heat degrades the cell rapidly. 

Let's change the supposition...

Suppose we are using high current cells in a high current application. Take a look at these cells.

It looks like 3 minutes at 20 amps will result in the same 50% state of charge that 30 minutes at 2 amps will. After 3 minutes at 20 amps if the resting voltage ends up at 3.85 volts, we have cells at 50% state of charge with a voltage of 3.85 volts.

It is interesting to observed that there is a recent push to store high current LiPo battery packs at 40% instead of 50%. 40% state of charge has a resting voltage of 3.7 volts.

Tom


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## Overclocker (Mar 8, 2017)

SilverFox said:


> Hello Gauss163,
> 
> If I have a drone that has 20 minutes of run time and fully charge it and then run it for 10 minutes, I should be at 50% state of charge. Even if the resting voltage of the pack is showing 3.85 volts per cell.
> 
> ...





Tachead said:


> And yes, your method works well.






20min runtime implies high current draw. depending on the drone's LVC (low voltage cutoff) you might not get all the juice out from the battery because high currents induce a large voltage drop, so LVC might be reached prematurely.

a better way would be to do a FULL discharge using a hobby charger at 1c or lower. note the capacity. then do another discharge that only drains half of the capacity. that would be your 50% soc

depending on the chemistry e.g. NCA going from 50% to 60% storage SOC already entails a significant hit in capacity loss, at least according to this study.


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## SilverFox (Mar 8, 2017)

Hello Overclocker,

I agree that it is important to know how your particular application works. With the cells that I referred to low voltage cut off was not a concern.

Looking at the charts you posted it looks like the difference between 50% and 60% state of charge is a little under a 1% drop in capacity. This brings up the question if a 1% drop in capacity over 10 months is significant to my use...?

Keep in mind that my storage is usually for a 5 days or less with flying almost every weekend and my storage temperature is always below 25 C.

Tom


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## Overclocker (Mar 8, 2017)

well i've already stated my position on the other page. for small packs it really doesn't matter. when you get to the larger vehicle packs that you may intend to use for years then small differences do add up

almost OT, i just finished wiring this up:


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## Gauss163 (Mar 8, 2017)

SilverFox said:


> While I agree with what you are illustrating with you supposition, it is flawed.



Please be more precise: what "supposition" do you disagree with?



SilverFox said:


> You are illustrating what happens when you use a high capacity cell in a high current application.



Neither true nor relevant. It seems that you are referring to the example I gave in this post, in reply to your question about SOC after running a drone for half of its _usable _capacity. Since it seems that the point of that example was not clear, I will elaborate below.

The point was to give an example where the _usable _capacity is much lower than _nominal_ capacity (at C/5 rate). Here the usable capacity refers to the capacity we obtain under actual use of the device, where the (average) current may be so much higher that then nominal (C/5 rate) that the pack yields much lower capacity than the rated nominal (C/5) capacity (e.g. this is typically true for the jump-start packs that you mentioned, and many other extremely high-current devices).

In such extremely high-current apps, when the pack is at 50% of usable capacity, there still may be much higher nominal (chemical) capacity remaining (but to access all of it we'd need to discharge at a much lower rate). In such cases it is only the nominal (chemical) capacity that is closely correlated with the _resting _(open-circuit, no-load) voltage of the cells during storage. It is this resting voltage that governs many of the degradation processes during storage. Thus SOC levels for storage guidelines always refer to percentage of nominal (better chemical) capacity, not the possibly much lower usable capacity. 



SilverFox said:


> Suppose we are using high current cells in a high current application. Take a look at these cells. It looks like 3 minutes at 20 amps will result in the same 50% state of charge that 30 minutes at 2 amps will. After 3 minutes at 20 amps if the resting voltage ends up at 3.85 volts, we have cells at 50% state of charge with a voltage of 3.85 volts.



But that's not an example of an extremely high-current app because the tests don't go up to high-enough current that the usable capacity starts diverging from the nominal capacity. If you take any cells to high-enough current they will eventually reach some point where the usable capacity starts dropping off dramatically (mainly because the IR drop will push the flat (low-slope) part of the discharge curve below the termination voltage, so much of the capacity will be delivered below termination voltage level).



SilverFox said:


> It is interesting to observed that there is a recent push to store high current LiPo battery packs at 40% instead of 50%. 40% state of charge has a resting voltage of 3.7 volts.



Yes, as I said, generally 40-50% SOC is considered a good storage level (but the exact voltages that correspond to those levels depend on the chemistry). Due to competition the RC/hobby manufactures are now being forced to provide more optimal numbers - even though doing so significantly cuts into their profit margins. This is exactly analogous to what occurred with laptop batteries, e.g. most all now have "battery saver" software, and analogous features have recently started to appear in the RC world, e.g. recent DJI packs have a user-configurable "auto-discharge" feature that will drain the pack to 40-50% SOC after a couple days idle (the number of days idle is user-configurable). Before this feature appeared power users jury-rigged their own devices to discharge DJI packs to what they deemed to be healthy storage levels, e.g. look up the Phantom Angel.


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## Gauss163 (Mar 8, 2017)

Overclocker said:


> [...] depending on the chemistry e.g. NCA going from 50% to 60% storage SOC already entails a significant hit in capacity loss, at least according to this study.



Thanks for providing further scientific data supporting my statements about the relationship between storage degradation and SOC. What is the source of those graphs? (they look familiar but I can't place them off the top of my head).


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## SilverFox (Mar 8, 2017)

Hello Gauss163,

My illustration was to show that some cells handle 2C discharge rates without serious degradation of capacity.

I showed cells that can handle 10C discharge rates without problems.

If the drone battery pack is constructed with cells like this and only subjected to 2C discharge rates, then running the drone for 10 minutes of the 20 minute run time will in fact discharge the cells to 50% state of charge.

I don't believe at 2C discharge qualifies as extreme.

To be perfectly clear...

I design an application that involves a 2C discharge rate and supply it with cells that can handle 10C without degradation in capacity. Running the application for half the run time will reduce the state of charge to 50%.

Back to the drone. With an expected run time of 20 minutes I can reach 50% state of charge by running the drone for 10 minutes. This assumes that the cells in the battery pack are high current cells that do not suffer degradation in capacity at 2C.

If after 10 minutes of run time the battery pack shows a resting voltage of 3.85 volts per cell, then 50% state of charge is 3.85 volts per cell.

Keep in mind that the original question involved storing for a week with flying on the weekends. My comment is to fully charge the battery pack and run it for half the run time and then keep it at a temperature lower than 25 C. Do you have any studies that show that storing for 5 days under these conditions will severely degrade the battery pack?

Once again to be perfectly clear...

Battery pack is made up of cells that are capable of 10C discharge without a significant loss in capacity.

Application runs at 2C.

Storage is for 5 days.

Storage temperature is less than 25C.

Tom


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## Gauss163 (Mar 8, 2017)

@Norm, Yes, if you are discharging at a rate that yields capacity close to nominal, then 50% of capacity at that rate will be close to 50% of capacity at the nominal rate. However, you need to keep in mind that if the load is not constant current (e.g. constant power), then 50% of runtime need not be 50% of capacity.


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## Overclocker (Mar 9, 2017)

Gauss163 said:


> Thanks for providing further scientific data supporting my statements about the relationship between storage degradation and SOC. What is the source of those graphs? (they look familiar but I can't place them off the top of my head).





http://jes.ecsdl.org/content/163/9/A1872.full


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## Gauss163 (Mar 12, 2017)

For convenience, below is a summary of the primary degradation / aging mechanisms of the anode and cathode in Li-ion cells. Notice in particular how high SOC plays a role in the majority of the degradation processes.


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## Gauss163 (Mar 12, 2017)

Excerpted from: Predictive Models of Li-ion Battery Lifetime, by Kandler Smith, NREL, 2014.


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## Gauss163 (Jan 18, 2018)

To expand on my remarks in post #5, here is some further data on the degradation caused by float-charging and storing at high SOC and high temperatures. Below is a graph from this 2014 study of calendar life degradation (no cycling) for Sanyo UR18650E cells stored at various SOCs at 50°C. As the study shows, you get only 107 days lifetime storing at 100% SOC, but 2.7x that (288 days) storing at 95% vs. 100% SOC, and 14x that (4 years) storing at 0% SOC.


Ecker et al. said:


> During calendar aging tests cells were stored at different SOC and temperatures. Fig. 6 shows capacity fade and resistance increase for cells stored at 50°C at different SOC. As expected, cells stored at lower SOC exhibit a longer lifetime. Especially cells stored at 100% SOC show a much faster degradation compared to other SOC. These cells only reach a lifetime of 107 days at 50°C until capacity reaches 80% of the initial value (linear interpolation). At this time the resistance increased by a factor of 1.3. For comparison, cells stored at 95% SOC reach 288 days until end of life (linear interpolation), whereas a cell stored at 0% SOC has an extrapolated lifetime of about 4 years (linear extrapolation of the last three measured data points)


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