Hello All,
about six or so weeks back I purchased a new Dualsky 3S, 11.1 volt, 2200mAh, 16C battery but I never used it till now.When I received it I discharged and charged it with a B6 charger and stored it away.It was my 1st Li-Po battery and about the same time I also purchased a few Zippy Li-Po batteries from Hongkong and I stored them too without using them. But today when I took out the Dualsky battery to put in one of my models I found the battery is slightly puffed. I inspected the Zippy batteries too and found them to be in the same condition when I received them. I have no experience with Li-po batteries. So I request the experienced flyers to advice whether it is safe to use the slightly puffed  but brand newDualsky battery or not.Is there a test to see whether a li-po battery is safe or not.Thankyou
Rgds
Rao.

First of all, you discharged the battery for storage, I think that was probably a bad idea.  Most manufacturers ship their batteries already in the "long term storage" charge (which is also known as "half charge", that is about 3.9v per cell).  You may have discharged it too much.

Now about using slightly puffed batteries, please note the following.

1) I used them for a long time, until I find they are not retaining enough charge to provide me with a reasonable flight time.  I guess they die a natural death over many usage cycles.

2) Do not use them if they are severely bloated (like each cell has become like 1.5x wide).

3) Watch them carefully when you charge a bloated lipo for the first time.

4) Remember that the biggest cause of bloated batteries are over-charging or over-discharging.  I feel that over discharging might be cause of the bloat in your case.

5) Remember that a bloated lipo will not give you the same performance (ie, duration) as a good one, keep that in mind.  So plan for shorter flights, otherwise you will over-discharge them again, and cause even bigger bloating.

6) Finally, if you are not comfortable with how the battery looks, then do not use it.

Raoji ,
My observation is there are 2 types of Bloating , for want of a better term I will call them soft bloating and hard bloating  .

Soft bloating : is when you can press the battery and it will be soft like as if air is filled in it more like sponge
Hard bloating :  is when it is like stone

Hard bloating is clear indication of battery damage  hence the only option is to dispose the battery

Soft bloating : battery can be used no issues but as Anwar says monitor charging.

In your case the damage looks to be due to you having discharged it to lowest voltage and the due to the fact that  batteries will normally loose some charge over a period of time the voltage has dropped below .

The best way to  check a battery is the LIPO checker which I use extensively
http://is.gd/U2ha

Attached Photo , I normally don't discharge my batteries below 3.5V  per cell.

The above is based on my experience of using LIPOS for over 2 years now , because of the publicity  against LIPO's most  persons get scared the moment the lipo shows any deformation from the original shape , but I have been using  soft bloated LIPO's 2 x 11.1V 4300 mah Zippy's with 22.2V usage on my tiger 60 for over 1.5 years now without any problems.

Sai

thank u very much for ur info. i bought 3s 1850mah lipo 4 months ago and i didnt know tat for long term storage it shouldbe 50% charged. i charged to its full and kept in cupboard for 3 months, thinking it will reduce it charge like NiCd or NiMH. but the he truth is it wont discharge like them. last week took my battery and checked it to be lightly puffed. am scared to death, to see it. saw some videos in youtube, lipo bursting like dynamite if we misuse the chemistry of them. now i know my battery is soft bloated as sai said, so no problem of explosions kind of . thanks anwar and sai, i could not get my sleep for a week. any how i should keep a close watch of these potential bombs.

can anyone suggest how to charge, store and discharge lipo in a safe way? like i saw some product like lipo safe bags.

I normally use a old Vanity case Or small Suit case for storing them.
BTW anything that delivers power has to have volatility  hence describing a LIPO as a bomb is taking it too far.

As I have said earlier is Nitro Methane Or Methanol not inflammable  without their ability to  explode and combust they will not be able to deliver power, its only that over sooooooooo many years  we have learnt to handle them , the same is true for LIPO's as well.

Sai

well said sai lipo are used everywhere, cellphones, laptops, cameras, rc models etc. we wont abuse the batteries in cell phone or laptops as we do for our rc models, as we crash, over discharge etc, which are not common on cell or laptops. hence i used the word potential bomb. take it lite

Dear Anwar and Sai,
thank you very much for your advice. Now I realised that my battery is slightly soft puffed. It feels as if it was filled with a little air. and the puffing is small about a cm or so I believe. As adviced I will pay extra attention while charging it.
Thank you
Regards
Rao.

OK, so how does one prevent over discharging or over charging in the first place? To draw a analogy with cell phones or laptops, we just plug in the charger and forget it for quite a few hours. So in the case of LiPo what is the way?

Pankaj

Hi,

Always ensure that you use a  good make (computerised) charger for charging/discharging lipo's. Its advisabel to use a balance charger like B6 or B8 to ensure that the cells are charged to the full and then cutoff. Computerised chargers have inbuilt circuitry to ensure that they do not overcharge/discharge.

As for the cellphones/laptops, they have inbuild circuit protection to stop charging the batteries once they peak out. Also, these are designed to ensure that the batteries are not deep discharged.

Cheers!!!
Saurabh

Pankaj ,
Lipo Charging is taken care of by most chargers including the simple ones .
There are essentially 2 types of chargers :
1) Variable charge rate : costlier
2) Fixed Charge rate : Cheaper

The charge rate essentially determines  the time required for charging .
eg a fixed charge rate charger operating at 0.8 amps will charge a 800 mah battery in 1 hour a 1600 mah battery in 2 hours etc . Now if you were to able to vary the charge rate  and set the 1600 mah battery to 1.6 amps charge rate then you can charge that battery in 1 hour and suppose you increased the charge rate to 3200 mah you would then be charging the 800 mah in 15 mins and the 1600 mah in 30 min, though this is not advisable .

Normally all chargers have a cut of set which does not allow battery voltage to exceed 4.2 V per cell. hence  they will cut off at max charge and give you an indication.

Sai

Going by the same logic, the ESC or some circuit should take care that the Lipo does not discharge beyond a certain point.

In that case what is the justification of statements like "take care that the Lipo does not over charge or over discharge"?

Pankaj

Yes They can be programmed to cut off at the low voltage point .
But generally you get a judgement based on time when you should land as the RPM will keep reducing as the voltage keeps getting lower as RPM is a direct product of the KV of the motor and voltage and assuming KV to be a constant RPM is directly proportional to voltage.
sai

Sai

Most of the good chargers (does not mean expensive) these days will tell you how many mah you are putting back into the battery while you are re-charging.  One good rule of thumb is that you should only discharge to about 80% of the capacity of a pack.

So if you have a 1500mah pack, fly it and time your flight.  Note many mah you are putting back when you are charging the pack.  If you put back 1200mah, that is good and you can use that much time as a safe limit for your subsequent flights.  Instead, if you put back 1400mah, that means you are discharging too much, and you are better off reducing your flight time.

Oh...oh...Too late for me...

I had a Puffed up 3s 2200mah 25C battery, thought it was too dangerous to use it...  Then  Short circuited them using a long wire,  saw the wires go into flames and 3 cells getting bloated and going into flames..

OMG , i have wasted that good looking battery... wish i had read this earlier..

Question:
1) How do we know, mah  that we are putting back in ?  Is it time x charging amps to get their to 80 % charge ??