Study of importance of charge equalization for LiFePO4 battery pack

Series-connected battery pack is usually used in some applications, such as electric vehicles (EVs), uninterruptible power supplies (UPSs) and the compensation of distributed power generation, etc. When the batteries charged or discharged, the over-charging or over-discharging phenomenon usually occur without proper protection due to the difference in internal impedance and characteristics when batteries were manufactured. Therefore, the charging equalization of batteries is very important and needs to be implemented. In this paper, four LiFePO₄ batteries in parallel are charged to 3.65V and pauses 30 minutes for rest. Afterwards, the LiFePO₄ batteries are connected in series and discharged with different C-rates. The voltage of each battery is recorded and analyzed. Finally, the necessary conditions and limitations for designing the charging equalization circuit are presented.