alexam3001

If this battery are new then try to charge them in parallel (5 days ...) with a modern power supply and limit the voltege to 3.45V. This will do a slow charge but all the battery will have the same SOC. Connect them in revers corner e.g + on left and - on right and after 2 days connect in oposite corrner. Depend on the bms, the balancer can be a resitive one  with mA or with active balancer A(1~4A). But this is not true !!!! The active works perfet aafter 99% of SOC, and because LifePo4 is linear aprox linera the active balancer is doing a small job. and 4A can not be reatch with 10mA voltage deviation. 
Concusion: fist try to charge in parallel to get the same SOC and the the balancer will do the job. 
I have 2x 5kW pack and for both i did the same, parallel charging. 
On normla oprtation the  SOC is form 95% to 20% ~3.4V (for 95% and 3.1V for 20%).