Below see two Node Red graphs of the charge curves for our 4 paralleled sets of 271ahr cells, 4S2P, using a low charge termination for now. We currently have our balancing set to start above 3.3vpc and at a delta above 20mv. Earlier we had the balancing set at your defaults.
In the first graph it appears that the delta did not get above 20mv until the cells reached about 3.43vpc. Had the balancer been working earlier it would have been pushing the green cell down even though that is not the high cell at cell termination. You can also see that the orange cell starts out low when the cells are at around 3.36vpc, and then goes high near charge termination. It is getting drawn lower by the balancer starting around 3.43vpc, while the green cell is high to begin with, then evens out with black and blue cells at charge termination. We are not sure what the green cell indications at about 3.45vpc represent.
In the second graph you can see more of the same as the orange cell goes from lowest voltage to highest. Then later the orange and green cells start to swap high/low positions at around 3.42vpc and as they approach charge termination, but before the balancer cuts in.
We can move the orange and green cells a bit closer to the black and blue cells manually by using our bench power supply and adjustable load. But I am not sure that any balancer would do that properly with these cells. Here is an explanation from another forum about this problem:
"When we reaching the charging shoulders, the cells with lower inner resistance are simply fuller and
overtake the balanced cell. The balancers switch to them, but have very little
time to fix the mistake they made in the first place leading to imbalances. The only mitigation is
to start balancing as late as possible, when the cells enter the shoulders and
leave them alone in the plateau phase". He has set his balancer to start balancing at 3.42vpc.
We are pretty sure that this is caused by the cells not being well matched for internal resistance and the change in internal resistance as voltage changes. There are no loose connections and there has always been this mismatch of charge curves with our RJ and now RJ/Lishen mix of cells. The same is true of the other 16 RJ cells that were bought with ours; the charge curves just do not exactly match. We suspect that this is true of most of the lower priced Chinese prismatic cells, but most users can't see it.
We think that the best course of action is to get the cells as close as possible manually, then raise the start balancing to just above 3.4vpc or wherever the cell voltage positions stabilize, and then reduce the delta to the default at 11mv. What do you think?