New lipos arrived today, but some aren't balancing correctly

[izeman]

i would charge all packs FULLY to 4.2v and let them sit for 1-2 days. then write down the voltage the cells dropped to. i expect that the same cells that came low will be lowest again. if not than you should be safe to use them. if not i would not use them in a big high power pack. i still use them for other tasks.
if you can do an internal resistance test then i would do that. it will identify bad cells easily.

 

[Ykick]

i would charge all packs FULLY to 4.2v and let them sit for 1-2 days. then write down the voltage the cells dropped to. i expect that the same cells that came low will be lowest again. if not than you should be safe to use them. if not i would not use them in a big high power pack. i still use them for other tasks.
if you can do an internal resistance test then i would do that. it will identify bad cells easily.

Yes, "leaker" test is very important.

 

[dnmun]

you really should not have to worry that they will self discharge when they are new cells since they test for that when they are manufactured.

 

[izeman]

So say you. If they really did you would never receive bad cells, wouldn't you?

 

[dnmun]

you can look at the pictures online for the machines they use to do the formation charge and test them.

 

[Ykick]

In a perfect world QC is 100% and there'll never be any "leakers". My world isn't quite so perfect and 'reckon I'm not alone. Such a simple and easy thing to do, why not record voltages and compare again in a day or two resting with nothing connected? Low risk but high reward should you ever discover a problem cell. Older they get, the more they change.

To confuse things further, BMS cell balancing circuits commonly short on my wire/plug installations. They're practically useless (80mA) for large capacity cell groups IMO so I usually remove anemic balance resistors and ignore that feature. The hat trick is to find shorted balance transistors before they duff your cells. This is different from a "leaker" cell however.

 

[dnmun]

the problem you have is not the resistor. the mosfet used as the shunt transistor is damaged by static electricity from handling on the gate or if the sense wire is connected to a voltage higher up in the battery than the breakdown voltage of the mosfet. the resistor has nothing to do with it. it is easily repaired by replacing the mosfet.