How many of you charge your LiPos to ''storage'' voltage when not in use?

General Discussion
#1

Hi there! It seems that this topic comes up again here and there.

So what is your opinion on this - for how long a fully charged LiPo battery should be kept this way?

I’ve heard some ppl / sources saying only like up to 2-3 days… when some, mention that a month is also okay and nothing to worry about…

I understand that this is a topic which is pretty hard, almost impossible to be verified on your own - whenever keeping LiPo’s fully charged has any effect on their cycle life - but I wanted to hear the opinions and perhaps some others sources you have come up with!

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Im not sure how much does info related to Li-ions, for some reason I believe they are not as suspectible to this… but, perhaps, also should not be kept at full voltage for over a year…

Hence - the reason why cells are shipped with low voltage… both for longevity and safety (less energy in them).

A bit background info from a guy who seems to be dealing with LiPo’s for a long time:

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Source: http://www.rchelicopterfun.com/rc-lipo-batteries.html

It is understandable that some of these guys use smaller size batteries… but non the less, I think this is pretty ‘‘chemistry related’’ so yeah, I wonder how it really is… have not heard it mentioned much on this forum, honestly… that one should not keep their battery charged at full all the time :slight_smile:

#2

I never leave my Lipo/Liion fully charged for more than a couple of hours. If I charge too many batteries before I go fly and get home with a few fully charged, I’ll return them to storage.

#3

Good for you! @PXSS That you take care of your batteries in such a way.

I found another document:

http://uterc.org/files/LipoStorageTips.pdf

The numbers are quite staggering here!

I will try to look up from what tests / batteries these numbers are taken! If I were not reading endless sphere occasionally, I think, I would not have stumbled upon this so early.

Btw, battery bro has also some good insights. I know they are not 100% scientific probably but they deal with batteries, so they should know a thing or two about them, for sure:

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The question now is - what is considered ‘‘long term’’ storage for li-ions?

In the article they mentioned 3 time periods… 1-3months… so should it be considered 1month or 3 months?

Anyways, from this I think it is clear, that it is not wise to keep the eboard’s battery (or any other lithium battery) charged fully at the end of ‘‘season’’ if you not use that battery/board for a while :slight_smile:

#4

A bit side-related but interesting:

Source: http://batteryuniversity.com/learn/article/bu_808b_what_causes_li_ion_to_die

#5

A lot of the research done in this area is quite dated so take the information with a grain of salt. Specially for Liions. I think the last paper that had numbers like those was like 10 years old? I’m doing my own research on the topic but I am not allowed to share results or talk about it as it is tied to government property.

#6

@PXSS I know. It looks like there are not that many Public Li-ion research papers with easy to understand information (tables, pictures etc…)

Too bad a lof of that is kept at the inside of the many companies, I believe… who have their own research teams etc…

#7

Do your own research… :wink: Buy 6 cells, charge 3 of them fully, 3 of them on storage, leave in box. Take out the first pair at the 6month mark, then another pair after 1year and the last after 1.5years. Measure their capacity before you put them in storage and after you take them out.

My boss would really not mind me sharing the info. Blame the government lol

#8

hah you should find a way how to ‘‘flood’’ the info out… :smiley:

at the same time not giving out the specifics… it’'s a matter about the principle anyways… and we would need some figures (numbers) to base our actions on…

Otherwise… I dont want to make ppl ape shit crazy about discharging their lipos to storage for that very reason… that they might lose a few % of their max capacity in a year’s time…

Though from what Im reading it looks like cells dont like high voltage at all… so all the time they are spending in 4.2v is actually harming them a bit… and best way to avoid this is just charge till 4.0-4.1v if possible… and leave the ‘‘main voltage’’ to perhaps around 3.9v and just ‘‘top it off’’ when in need…

#9

Yep. That’s pretty much what I’ve been trying to say. It’s not really the heat that kills them, yes it’s part of it but it’s not the only reason. The chemical reaction hates high voltage conditions and high charge rates.

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#10

Hi O,

I’ve been using LiPo’s for years in other interests. IMO they should always* be stored at storage voltage (3.85v per cell) Ideally you should only fully charge them just before you intend to use them. *This isn’t always practical so some middle ground has to be sought. So, I never leave them for more than say 8-12 hours fully charged. If I end up not using them I discharge them back to storage voltage with a homemade rig using truck bulbs (lamps) and a timer. Note, the timer is important. Over discharging them will destroy them instantly.:open_mouth:

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#11

@AndyPG I am curious what your homemade discharge rig looks like?

Good idea!

#12

Hi J,

It’s not a pretty thing. It consists of two 24v truck headlamp bulbs in parallel and several 12v stop lamp bulbs in series pairs. There’s a couple of old heavy duty resistors too and it’s all hot glued to a piece of wood. It draws around 10A and brings my pack down to storage voltage in about 25mins. Please don’t make me photograph it…it’s shameful.:blush: I know you can use a charger to do the job, but I prefer this method.

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#13

hah, cool that you have ‘‘picked up this trait’’ along the way :slight_smile:

I actually did not know about such thing once I started to ‘‘go into batteries’’… It kind of changes the whole concept of battery technology and using them in general…

I imagine the best situation would be to have some sort of ‘‘automated’’ (bluetooth or wifi connected rig)… which you can ‘‘enable to start charging’’ from you smartphone…

Let’s say… you are heading home to grab your eboard… and you push a button on the smartphone’s screen to start charging the batteries (assuming they are all connected or in an eboard’s stand at home)…

This way saving the time and hassle of connecting them and waiting till they get charged up. Wont talk here about leaving batteries unattended or such… but I just see this as a ‘‘smooth’’ way on how to make the charging process easier and less ‘‘labour’’ intensive.

I had this question on another forum: What could be the ratio between ‘‘forced discharge’’ to ‘‘damage done’’ while keeping the batteries charged?

This has troubled me a bit… as I am aware that discharging from full battery to storage voltage does count as discharge and goes to the total lifecycle count of the battery… so if this needs to be done often, like every other day… then I assume it could get counter-productive for the batteries…

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So far, the best scenario seems to be to charge batteries till storage voltage once they are empty / depleted… then, before actually riding them, try to start charging them 0.5 - 1h before the ride…

#14

I have a 36-42V charger that has a dial so I can set it to either storage or full charge through the BMS without needing to monitor it. There are RC chargers with bluetooth adapters too. FlyRC is the brand iirc, don’t think they have wifi enabled ones though.

#15

Agreed. You can always charge them at 2C if you are desperate. (And have a charger that can do it) Generally accepted that it won’t hurt every now and then.

#16

@AndyPG Yeah, this seems to be the way to do it… to avoid keeping the batteries charged at 4.1-4.2v when actually not in use for a prolonged period of time (1+ week)…

It is quite easy to charge the batteries up and then dont use them for quite a while… and actually forget they got charged up in the first place…

One more option im seeing as viable is to charge while ‘‘on the go’’… though, this requires that the board /batteries are taken along with you in the car and then charged there…

This depends on riding time also, of course…

  • I still got to figure out what adapter to make for charging from car outlet… Im not sure was the wires the fault… but the voltage kept going way too low… even at 2A charge rate (6s mode) and I just got a DC too low warning, even if low voltage cut-off was at something like 10.5v

Though, there was no regulation for the incoming voltage to the charger… I assume 1 or 2 caps wouldnt be bad, to try to stabilize the voltage a bit. since it was just a plain small directly wired dc jack, with some shady contacts at part, which connects to the the car outlet, with no electronics in between :slight_smile:

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@PXSS Will take a look at these bluetooth chargers. Perhaps they offer some interesting features. Also sounds like you got a pretty nice / adjustable charger :slight_smile:

#17

Won’t hurt LiPos to charge at 2C, Liions will definitely not like it. Most spec sheets state standard charge at .5C and max at 1C, and they get diminished life from charging at 1C

On the go charging idea: there are some chargers that can use batteries as your power supply. You could hook up a LARGE Lipo pack to your charger to charge your board from while on the go and then have the lipo pack hooked up so that its always at storage capacity.

For example a 3S 40Ah Lipo pack in trunk, at storage can charge up to 6Ah 10S pack before being empty. If you have a 10s4p 25R pack, that is 60% capacity you can charge on the go.

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#18

Hi PXSS, Agreed and good to remind readers that the thread is about LiPo’s not Li-Ion’s.

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#19

I changed the topic name a bit but I think we can apply the same principle to li-ions, too (not keeping them at 4.1v).

Although it seems that Li-ions are somewhat more robust compard to lipo’s in general, even if it is not as advised to charge them at 2c rates or discharge at high c rate.