Hey all. A couple months ago I put together a 560Ah 12v pack (2p4s) using the 280Ah Eve cells (It is possible that I actually have the 272ah Lishen cells....the vendor on alibaba was a bit unclear).
Today I was charging up the pack from ~60% to 100% using my victron compact multiplus 12/2000. The charge rate was ~70A, and at around 80% SOC I noticed something strange. The voltage on one of the cells (actually 2 parallel cells) in the pack was rising and quickly hit my BMS cutoff of 3.65v. The other 3 cells were all around 3.35v. I figured that maybe I have a weak cell or they somehow got out of balance.
In order to keep charging I reduced the charge rate to about 15A, which kept that first cell voltage from hitting the cutoff. It hovered around 3.55v for almost the rest of the charge cycle while the rest of the cells stayed at ~3.35v. However at about 98% SOC when the other 3 cell voltages started to rise, the voltage of the "weak" cell dropped down. All four cells are now at around 3.45v, with the weak cell just slightly higher at 3.48v.
Is this normal behavior for a weak cell? Why would the voltage spike high earlier but then drop back down as the pack nears 100% SOC?
These voltages are measured by my BMS (daly smartbms) in case that is a factor...