I use a LFP battery with 2nd life cells in a 2x8 configuration, delivering (supposedly) 240Ah at 26V = around 6.2kWh. In South Africa, reasonably priced new cells are unobtainable due to exorbitant shipping costs. So, I am trying to handle the used cells gently in order to maximise lifetime. I only use around 50% if the full capacity, charging to 75% SOC (3.4V/cell) and running them down to 25% SOC. Current drain is around 0.1C with about 2 min of discharge at 1.4kW each day. I use a capacitative active balancer (max balancing current 2A) in parallel with one of the older types of Daly BMS devices. My problem: see attached image. Despite top balancing to 3.65V/cell, the cells rapidly become unbalanced while charging from the solar panels. After less than an h of use afterwards they drop to similar cell voltages. Swapping the three bottom cells with the 3 topmost cells does not provide a solution. Thus the problem is not related to specific cells, but to the charge/discharge regime of the battery. My question: is there any obvious way of improving the cell balancing during normal use of the battery?
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