LiPo Question: One cell doesn't fully charge

[javaboy]

I've got a 4S 6200 battery that has one cell that won't fully charge. I've re-charged it a couple of times and the questionable cell only tops up to 86% while the others seem fine. Question: how poor must a cell be to consider the battery not worth using? Also, is it possible to rehabilitate a battery cell somehow? I am sure this occurred due to an inadvertent over-discharge. All of the other batteries from the same lot are fine.

Thanks.

 

[Bartman]

javaboy,

is it a new pack? if so, run it and then charge it a few times. sometimes that will get the cells all performing more similarly.

you could also try to discharge the other cells to the level of the one weak cell. once they're all close to the same voltage the balancing function can keep them together better. discharge cells using a flashlight bulb or some other low draw load through the balancing tap so you only tap the cells you want to discharge. if that's too much to figure out then just fly it a few times and see if it recovers on its own.

bart

 

[BorisS]

hmm i dont understand the 86% calculated from 0 - 4.2V, specific to one cell ? that would mean one of your cells only reached 3.6 V. If this is the case i wouldn't fly with it !

Boris

 

[RCNut]

I recently bought a 3600 mAh 3S pack that had one unbalanced cell. On the charger the two outside cells would reach 4.20V but the inside cell only reached 3.95V. After checking with the supplier I was told the cell voltage difference wasnt large enough to warrant replacing and I should cycle it. So I ran the battery through two discharge/recharge cycles (using my charger's discharge feature) and it is now fine. I've since flown with it and haven't had any further issues with that cell and flight times have been good.

In the process I found it was necessary to bring the good cells down to a similar voltage to the bad cell before recharging. Simply trying to extend the charge time when the good cells had peaked didn't fix the problem.

 

[kloner]

I wouldn't fly a pack with a difference of more than .2v....... that is the sign of super high internal resistance, ie, dead pack. usually if i can't get a pack to hold more than 4.17-4.18 a cell, looking at internal resistance is in double digits. if you did fly it, expect alot less flight time and for it to progressively get worse fast. if you get a new pack with cells off, you want to exchange it or throw it away. it'll never totaly be good cause the IR is already fubar

 

[DucktileMedia]

out of 12 batteries I have had 2 now that had this same issue. the first one I ran 3 times and it started charging to a full 4.2. The latest gens ace 4s 4000 I got has a cell which still wont come back up so I think I may return it. Sucks though as I soldered my deans to it already.

 

[kloner]

with hobbypartz and hobbyking, when you get a pack you have to decide if your keeping it or sending it back. only way i know how is to use a cell checker cause you gotta do it before you alter it. if you get a pack that's off more than a couple tenths i'd call em right away and just send it back. I've seen em both fight ya to the ground over a bad pack that's altered. Both are pretty similar in CS

the problem is you can kill a cell in one flight not used right, and that's the position they usually take once you tell em it's screwed up and altered/used

 

[javaboy]

Thanks for all the good input. I remembered that my little battery tester (Extreme Power Analyzer) has a cell balancing function on it that I've never used. It took an hour to balance but it finally did and then I topped it off with the charger and it fully charged with all cells perfectly balanced. I've flagged this battery so I can watch it closely and I'll use the Quanum in-flight monitor to watch the cells when I fly Saturday. Hopefully all will be fine now.

 

[RCNut]

Yes I wrote a small X on my dodgy pack with a permanent marker so I could keep an eye on it. So far it's holding up well.