LiPo odd behaviour

[BuggyDad]

One of my LiPos seems to be behaving strangely. 

It was used, down to as low as 4 or 5% on my charger display, which I think is low but not crazy low - low voltage cutoff ESC did its job. I didn't note the cell voltage at this point. It was I guess about 3.7v. On storage charge my charger is set to a charge current of 3A, yet on this cell it would charge at only 0.4A, as a result not bringing the charge up much at all and eventually timing out. Repeated it, switched sides of the (dual) charger, compared it with another, and it seems to be this battery. Others the charger just takes up to 3.85V ish. It does vary the charge current but not this low and I guess this is about balancing and/or slowing down the rate at key points in the cycle. 

Subsequently I put it on balance charge for a short time to get it up to storage voltage and it did that seemingly almost instantly, like the charger was reading a different voltage when set to balance charge vs when set to storage charge, or when applying a higher charge current rather than a low one. Then I ran the pure balance function for a bit, and the voltages of the two cells are now equal. 

I've been OK with LiPos so far (no expert, I simply always make sure to store them at storage voltage, balance charge when I charge them up and never run them below cutoff; charger jiggerypokery beyond that I don't know about) but this confuses me. 

The battery is (sorry!) a cheap Gartpot one from Amazon. I have a few of these and also have a feeling (but no data to back it up) that they aren't the greatest. Just a sense of slightly lower power mainly. 

[ChrisRx718]

Mate it sounds like-for-like how my weekend went with a Turnigy roundcase LiPo, very similar behaviour. Had been in storage a long time, I ran the battery down to LV cutoff then tried to re-storage charge it and noticed a big discrepancy between both cells. 

Charged just fine in the end on 'LiPo Balance' setting, taking it all the way up to full capacity / 4.2v per cell. I intend to run it again in the next few days to see how evenly it discharges.

Nothing peculiar about how it behaved once in the car though, all went well.

I'm not worried, yet. But I'll be keeping an eye on this thread! 

[alvinlwh]

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[one_hit]

After running the battery, check the individual cell voltage on your charger (usually called battery meter, or can be displayed by pressing + while charging). Most likely the voltage difference between the cells is too high, causing it to take a long time to storage charge or balance charge. I have two batteries that are like this, they both take a long time to storage or balance charge on my SkyRC D100 and T200, but not on my T1000. This is the difference with the cheaper or older chargers - the D100 only has a balancing current of 200mA, the T200 has 500mA while the T1000 can balance up to 1.5A. 

[ad456]

Is there any fat bits on the battery wires that may suggest a damaged cable? Is it a different set of cables for the charger on the “other side”?

@alvinlwh that’s a good shout on a dirty connection, that would definitely encourage weirdness. 
 

A multi meter might be a sanity check that it’s not the charger itself. 

[simalarion]

 

[Willy iine]

It sounds like the cells are unbalanced, but who knows.   When I run LiPo I only go down to 3.75v as it will bring up the charge level to 3.85v range after a short rest which is within range of storage voltage.  
 

LiPo has great performance benefits but a high maintenance chemistry so I haven't used mine in years.. like over 5 years.  They sit in my metal trash bin inside their heat safety bags monitored every 3 months for storage voltage. 

[BuggyDad]

Yeah I think I will keep an eye on especially these Gartpot ones for their balance, although I don't recall it being much more unbalanced than I often see. My charger has a touchscreen and I habitually run it on the display that shows the cells individually. On this one it just didn't want to put the normal current in. After getting it to storage voltage I did also run the pure balance function, leaving the cells equal, although before doing that they were already as close as I expect from my other packs.

The plugs seemed clean. I've had that issue before. 

I'll mark this pack too, and watch it closely next time I use it.