I charged two Lipo batteries and then the weather decided I wasn't flying that day. Does anyone know if it is ok to leave them fully charged for say a week or two with out doing any damage to the battery? The batteries are 11.1 v 25c 2500.

Not really a great idea.

http://www.rcgroups.com/forums/showp...61&postcount=1

Did you link the correct post? I don't see anything in there that gives evidence as to why it's a bad idea, just a recommendation on how to store them. For sure it's a bad idea long term, but will we really see any perceptible difference in just a week or two?

It has been found that even a day will degrade cells some. The higher the C rating the faster they degrade.
Even one of the battery guru's of yesteryear put his tail between his legs last year and agreed with everydayflyer by admitting he was wrong.
If you want it in black and white buy two 3s high C packs, seperate the cells so you have 6 cells and test away...or just take edf's advise and save time and $$$.

Rick

Originally Posted by rampman

It has been found that even a day will degrade cells some. The higher the C rating the faster they degrade.

It has been found where? Got a link?

Even one of the battery guru's of yesteryear put his tail between his legs last year and agreed with everydayflyer by admitting he was wrong.
If you want it in black and white buy two 3s high C packs, seperate the cells so you have 6 cells and test away...or just take edf's advise and save time and $$$.

I'm not saying he's wrong or even arguing with him (or you). I'd just like to see the info that backs it up. I'd rather not blindly trust internet forum "common wisdom". It's the engineer in me.

Thanks for the advice, I think I'll err on the side of caution and discharge them to 3.85 volts per cell every time. What a pain in the butt!

Perhaps RC Groups need a certification program for posters.

Go here and read the notice in bold type under each LiPoly's decription

http://www.xtremepowersystems.net/products.php?cat=16

Go to the Battery Graph Vault and wade thru my test on Lipolys over hundreds of cycles and over a three years storage test period.

Take the easy way out and treat them as you wish as they are yours. Some enjoy repalcing Lipolys often but some pay top dollar for the best and expect them to last .


Gio here and see what a pioneer in LiPoly sells had to say.

http://www.rcgroups.com/forums/showp...&postcount=994

The long version for those who do not know how to open threads

http://www.rcgroups.com/forums/showp...&postcount=991

Snip:

PS: As an aside, we have recently completed some long-term (14 months) Lipo torture testing (various brands, inc. G3), for range of temperatures, STORE voltage, etc... We were rather astonished to find how badly storage above 25C affects all Lipo lifespan, and in particular when temps are sustained above 30C (which is why laptop lipo fail so fast. Hot environment, and almost always at 100% charge). The issue is more serious the lower the Ri of the battery (higher C)

Charles

Well if I want a good steak I could stick my head up a bulls arse and see for myself or I can just take the butchers word for it....I think I'll take your word for it Everyday flyer. you seem to be the knowledgeable butcher here.

Originally Posted by Billtheboss

Well if I want a good steak I could stick my head up a bulls arse and see for myself .

I've never had bull rectum, but when it comes to batteries you can rely on Charles' info. When I decide not to fly a full pack, I just drop it in the plane and run it full throttle. You'll bring it down to storage voltage in no time at all.

What about Lipo transmitter batteries? A bunch of guys use them, and they get stored at high percentages of full charge. I understand they are low discharge C rated.

Some guys with the DX8 4000Mah lipo go a month without charging.

I use Sanyo Eneloops in my Transmitters and a couple of transmitters which I seldom use often go 6 months or more on a charge but to get back to your question.

LiPolys used in Transmitters or other extremly low drain applications do not suffer issues with high IR. Most Transmitter LiPolys are only rated 2C or so and most transmitter place less than a 1/10C load on them.

Improper storage causes LiPolys to develop higher internal resistance faster. A high C one becomes a lower C one. If you use a 20C LiPoly in a Slow Stick and get 20 to 40 minutes of flight time it really does not matter much how you store it. It will still work fine It may puff and lose some capacity but most would still find its' performance OK.

If you purchase 30,45,50,60C LiPolys because you need the performane and you do not keep them at Storage when not being flown they will lose performance before you get many cycles out of them.

Remember not all flyers have the same needs. Some purchase only low cost LiPolys and could care less it they last more than one summer of flying.

Some purchase very expensive LIPolys and would prefer to get two or three years (seasons) of useage from them.

Some like mysellf fly perhaps a thousand flights a year and some fly 40 at most.

Charles

.

Originally Posted by everydayflyer

http://www.rcgroups.com/forums/showp...&postcount=991

You left out the part where he says this:

That does not mean that if you regularly let them sit for a day or two fully charged that it will have drastic negative consequences. There may, or may not, be a measurable reduction in lifecycles. It is simply "best practice" to keep them at STORE voltage whenever you can.

If you do want to keep them charged for a few days at a time, you can reduce the risk by keeping the packs cool (say 10~20 deg. celcius)

Do people really fret about having them charged for hours, like the day before?

Originally Posted by ToBeFrank

Do people really fret about having them charged for hours, like the day before?

Yes, I've already had to dispose of a $125 battery for nothing more than leaving it fully charged.

Keep track of your cell IRs and you'll probably "fret" soon enough.

ToBeFrank

You left out the part where he says this:

Left out ?. I posted a one paragraph snip and titled it a snip. I provided the link to the complete post which give a fairly lengthy detail post on a 16 months study conducted by AirCraft / Hyperion.....................................
I am not going to post a page to try and prove a point to you as you have decided I am clueless and you are a LiPoly expert.

I am going to do you and myself a very large favor and add you to my ignor list.

I could care less how you miss mangage your LiPolys and those who to follow your lead will make better LiPoly customers for their prefered vendors as they will be purchasing more often.

Good bye

Charles

Originally Posted by ToBeFrank

Do people really fret about having them charged for hours, like the day before?

I'm not aware of any surveys on that subject which is what would be needed to answer that question.

I've read many technical articles that concluded that storage at a 100% charge level greatly shortened the cycle life and resulted in capacity loss. All were long term exposure to full charge conditions.

Consider this for the sake of argument.
We know that the loss of cycle life/capacity is not recoverable, it is an irreversable reaction.
Considering that, can it be concluded that every second under a full charge stress is taking some amount of "life" from the pack? I would think so. Is the degree of degradation independent of the battery charge state between full charge time periods? Does 24 hours of full charge stress cause the same amount of damage whether done in 1 hour increments or all at once? I'm not aware of any studies done on that basis, however, the satellite 'people' did research on using li-ion batteries and concluded that the charge level should be maintained between 3.8 - 4v for maximum cycle life which might support the 'all full charge stress is additive" argument.

Adding to the complexity of the subject is that manufacturers are probably using proprietary solvents which may influence how sensitive their cells are to full charge degradation.

In my experience, todays packs are more sensitive to full charge storage "puffing" than those from a few years ago.

Do people fret about it? Some do, some don't.