I have a one-year-old 48V 20AH Yesa LiFePo4 battery pack which has gone significantly out of balance. After a typical charge, the three batteries at the positive end of the string are over 4V, the middle batteries are at about 3.3V and the three batteries at the negatave end are all about 3.4V. I have tried using an individual battery charger to charge the middle batteries to about 3.7V but after a short time they come down again to 3.3V.
Anyone out there have any ideas on how I might re-balance this set? All the batteries seem to hold a charge ok.