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What can cause a Lipo to decrease max capacity?
#1
I've got a Tattu 1550mAh 4s, 2 Turnigy 1500mAh 3s and 1 Multistar 1400mAh 4s battery that have all decreased their maximum capacity per cell in the last few weeks alone.  
They all used to hold 4.19-4.21 per cell.  Now all of them are between 4.15-4.17.  
All of them have been used maybe 3-5 times a week for about 4 months.
I did leave them all fully charged for probably 2 weeks without use, and I have also changed my PIDs and Rates and started flying much more aggressively in those last 2 weeks.  
Would either of those cause this?

What's the best practice for charging/discharging?  How long is too long to leave a battery fully charged?  
I just purchased 3 new batteries and I'd love to make these last.
#2
A couple of things can and or will cause the Lipos to degrade.

1. constantly running them below 3.3 volts per cell (which I am guilty of..lol) Lipo alarm set to 3.6v per cell ( loaded), but I have to fly just that little bit more.
2. The amount of charge cycles the batteries have had.
3. Having them fully charged for long periods will make the first flight again shorter ( but I have found once fully charged again they appear fine.
4. Heat.. excessive aggressive flying will heat the battery a lot and make it swell up... Not good for it.


Lipo's are costly, but are also disposable items, they have a limited life span (with some makers claiming 1000 cycles, which I call BS, as I have never got even close to that figure.

How long is too long to leave a fully charged lipo for? Maybe a week or so, Generally I charge mine back to storage if I feel I will not be flying for a week or more. which is not often.
My youtube channel

[-] The following 2 users Like BigglesFPV's post:
  • tozes, Oscar
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#3
I mostly agree with Biggles BUT I would not leave a battery fully charged for more than one day.

Made the experiment with some 2200 50c+ 2s Lipos for and rc-car.
Battery 1: NEVER! stored fully charged, always stored at 3,75V ish/cell. I got 183! cycles out of it, it started to puff badly after that.
Battery 2: Charged in the evening to use it the next day. Stored around 3,8V/cell when I didn't use it for 4 to 5 days. 79 Cycles, than heavy puffing. 

A German guy from http://www.elektromodellflug.de/ stated that you should never store lipos charged, not even for one night. A rule wihich I do follow and I still have crappy Ziippys for some of my rc-cars which lasted for 150+ cycles (of course you notice shorter driving time and not as aggressive punch).
Then again I you ask two blokes on how to store/chrage/treat your Lipos you'll get at least two opinions...

I'd go for the safe route and store my Lipos at 3,7 to 3,8V to be safe because a fully charged Lipo can cause more damage than one which is more or less empt.

Just my 2 cents...
Build - Fly - Crash - Repeat
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#4
Stupid question,
as you are charging them ... you do balance the cells from time to time or only charge ?

when i did charge charge charge... i've had similiar results, now from time to time i do balance on single battery (not parallel charging) and the 4.20 is back on.
All the best
Grzesiek (Grisha/ Greg)

Curently flyable: Nox 5, Nox 3, Minimalist 112, Scrap at the moment... nothing is flyable
Bench / in progres: fixing Nox 5, Nox 3, Minimalist 112, Scrap
thinking about building: 450

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#5
(18-Sep-2016, 08:43 PM)Grisha0 Wrote: Stupid question,
as you are charging them ... you do balance the cells from time to time or only charge ?

when i did charge charge charge... i've had similiar results, now from time to time i do balance on single battery (not parallel charging) and the 4.20 is back on.

If that question was for me: I always balance charge.
Build - Fly - Crash - Repeat
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#6
@Grisha0, I actually tend to only balance charge.
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#7
AFAIK every charge/discharge cycle reduces capacity to a small degree - that's just how lipo's work. They're not perfect.

What makes it worse especially is fast charging and over-discharging.

Personally i only use a timer with enough safety margin, so if i know i'll go fly next day i fly a little longer, if not, i land quick and once the battery recovered from load, they're pretty close around 3.7v/cell so i can leave them in a corner 'til next WE.
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