The battery equalizer is used to maintain the charge and discharge balance between the batteries in series or parallel. During the working process of batteries, due to the difference in chemical composition and temperature of the battery cells, the charge and discharge of every two batteries will be different. Even when the cells are idle, there will be an imbalance between cells in series due to varying degrees of self-discharge. Due to the difference during the charging process, one battery will be overcharged or over-discharged while the other battery is not fully charged or discharged. As the charging and discharging process is repeated, this difference will gradually increase, eventually causing the battery to fail prematurely.