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Old Oct 25, 2010, 01:36 PM
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rotagen's Avatar
United States, CA, Felton
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Storing lipos in the freezer ?

Just wanting to get a general idea of how many people store their lipos in the freezer, and if so, what are your experiences?

Had my first lipo failure this weekend and since I don't get to fly nearly as often as I want, my lipos are stored for months at a time. And I realized I was storing them completely wrong. Room temp storage at full charge is about the worst thing you can do, it causes rapid loss of capacity which is what I experienced.

So from the chart here (which I have seen posted elsewhere) it seems that freezer temps and lower voltage (3.7 per cell or so?) will greatly slow the degradation.

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

I remember another chart which showed both 4C (fridge) and 0C(home freezer) temps and I think there was a big enough difference in decay to justify storing in the freezer.

Apparently they can be stored at in a -20C freezer and still work (at a reduced ability), here:

http://www.exa.com.tw/exa/characteristics.htm

Since there is no liquid electrolyte apparently.

I'm still a bit paranoid at storing them in the freezer but these things arent cheap, and I want to extend their useable time as long as possible.

So please chime in if you have experience with freezer storage, I'm thinking zip lock bags is good enough if you let them warm before use to stop condensation. thx.
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Old Oct 25, 2010, 01:54 PM
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United States, VA, Virginia Beach
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Everydayflyer may chime in on this also but here is what I do and it works.

I store all my packs at 60% charge in a spare fridge in the garage. Many of my lipos are two years old and still useful. I had two 3s 8000 mah packs for my telemaster last three years and were still going strong when I sold them.

On the other hand I have two 2s 2200 mah packs we use in our micro RC cars that never get charged to 60% and stay in the garage all the time in the heat. They have about 60% left in them and they are less then a year old.
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Old Oct 25, 2010, 02:58 PM
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United States, WA, Seattle
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It appears your first link used this chart:
http://batteryuniversity.com/learn/a...ased_batteries

There is only a 2% difference between O*C and 25*C at 40% charge.
I use the fridge, anything from 3.8-4.0v/cell for short-term storage and if I think it'll be out of use awhile go for 3.85v/cell.

I think the fridge is easy and safe, freezing might have more problems and not much benefit.
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Old Oct 25, 2010, 07:52 PM
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Yeah, wish I could dig up that chart I saw that also had a 4C figure. I'm thinking the difference between 4C and 0C might be too small to justify the hassle.

That was exactly my experience Mike, and I'm having to replace most of my lipos because I stored them at full charge room temp.

I've read they should be cycled once per month, but I doubt I will hassle with it. 3.7 or 3.8 in the fridge sounds reasonable.
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Old Oct 25, 2010, 10:00 PM
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^ whats the problem with freezing lipos? I keep them in a garage that gets well below freezing in winter time.

The air temp is freezing, but the lipos never "FREEZE" as in build up of white crystals (frosted).
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Old Oct 25, 2010, 10:35 PM
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Quote:
Originally Posted by rotagen View Post
I've read they should be cycled once per month,
Where have you read that?
Sound suspiciously like an artifact left over from NiXX and a bit of misinformation that is easily spread.

Men are still widely spreading the memory myth of NiCad. Read about it here....all the time.
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Old Oct 26, 2010, 07:11 AM
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Haralson County GA. USA
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Quote:
Men are still widely spreading the memory myth of NiCad.
Not a myth. They do have a memory. If you treat them badly they will remember and bite you in the ass.

Charles
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Old Oct 26, 2010, 10:58 PM
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United States, CA, Felton
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I actually read the NiCad "memory" problem in several reputable places online. Back when I gave a damn about Nicads and NiMh. I've always had way better consistent voltage and better capacity with NiMh rechargeables than Nicads, and I assumed it was due to the memory problemo. But I just read somewhere that NIcads last way longer when stored at room temp.

All I know is rechargeable AA batteries tend to suck, I bought a ton of them at one point, and they died so quickly I just started buying cheap costco batteries and chucking them. And I had a good trickle/smart charger. Bad for the environment cause I use a lot of them with my various guitar/music toys. I think they must get stored in a warehouse for about 5 years before someone buys them.

Battery technology will keep changing, I hope, cuz it needs to get better.
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Old Oct 26, 2010, 11:34 PM
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United States, IL
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You must not have heard about Sanyo Eneloop batteries then. Well worth looking into if you're looking for AA or AAA rechargeable cells.

As for LiPos, I store them at 3.85 volts per cell at about 60 degrees Fahrenheit. I also only charge them to 4.1 volts per cell, and only discharge them to about 3.75 volts per cell stabilized. I have some that are a couple years old and still performing well. Of course those particular ones don't have a ton of cycles on them either though.
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Old Oct 27, 2010, 03:53 AM
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Well you're saving your lipos somewhat by not over-discharging them, now if you store in the fridge or freezer at that voltage or a little lower (for long-term storage, months etc), you'll probably keep them for 4 years in good condition easily.

Sounds like u have a charger that gives you the voltage while charging? Programmable final voltage would be great! Hope my new one will do this for me.

I think I've tried eneloop, not sure, thx for the tip.
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