Can someone explain this strange cell deviation at float?

Capt Bill

Sailing Options
Mar 18, 2020
Redwood Valley, Cailfornia/ Montezuma, Costa Rica
I recently put together a 12V battery made from 280Ah CALB cells and an Overkill Solar BMS. This is my second pack I've made, but I'm seeing strange cell voltage deviation at float. While charging, Cell 4 tends to be the highest voltage compared to the rest, but fairly close in voltage. But when the charge controller hits a float voltage of 13.8, suddenly the cell voltages begin to deviate from each other. Cell 4 drops rapidly, while Cell 2 & 3 rise together. Rising voltage as the battery continues to absorb some charge is what I would expect, but all together. Cell 1 stays at a fairly consistent voltage. When they discharge, they quickly fall into balance again.

What do you think is going on??

My first guess are mismatched cells. Unfortunately because of a break up, and my ex being the one who ordered the cells, I don't know who the seller was or have contact with them to seek a remedy.

This is the second pack I've made, though the first was with EVE cells, and that one didn't exhibit any strange behaviors like this.

Could it be that they're not effectively top balanced? I was hoping that the BMS would slowly balance them at float like it did with the prior pack.

Would love some thoughts!

View attachment 70600
Wow ... Nice graphics of each cell voltage pattern posted by Balanceandpeace (first post of thread) ... first time I have seen the details for each cell. :+) Wondering what you figured out since awhile back. What resolved that challenge for you (if you see this)?
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