20S 7P pack made of brand new grade A Samsung 40T cells, now 6 month old, max current that was drawn from it was 140A peaks, got to 55C ANT BMS thermal cut off only once in it's life.
Then it sat on 3.9V per cell for a month with no use, suddenly cell row number 9 is at 3.0V while the rest are at about the same place they were when last used (around 3.9V) all perfectly balanced aside from row 9 which went down to 3.0V
So I charged row 9 to level with the rest and disconnected the bms to see if row 9 drops without the bms and it did.
It dropped 0.03V within 48 hours while the rest were perfectly balanced and dropped only 0.002V in those 48 hours.
Then I connected the pack to a load tested and pulled 80A from it for a few seconds and the max cell difference instantly went from 0.04V to 0.01V and stayed there after the load was removed.
What do you think can be the cause of that?
Then it sat on 3.9V per cell for a month with no use, suddenly cell row number 9 is at 3.0V while the rest are at about the same place they were when last used (around 3.9V) all perfectly balanced aside from row 9 which went down to 3.0V
So I charged row 9 to level with the rest and disconnected the bms to see if row 9 drops without the bms and it did.
It dropped 0.03V within 48 hours while the rest were perfectly balanced and dropped only 0.002V in those 48 hours.
Then I connected the pack to a load tested and pulled 80A from it for a few seconds and the max cell difference instantly went from 0.04V to 0.01V and stayed there after the load was removed.
What do you think can be the cause of that?