Battery equalizer is an energy transfer type equalizer that compensates for batteries in both directions, flowing from higher voltage to lower voltage. The battery equalizer can compensate for the battery in both directions, with low voltage disconnection to provide longer battery life. It can be connected in series for a long time in the battery system and automatically maintain energy balance in the battery state. The battery voltage balance system keeps the battery in good condition, maintains battery health, prolongs battery life, and reduces battery replacement. The battery equalizer has an intelligent voltage compensation system to keep the battery in an idle state and automatically shut down when the voltage is insufficient to extend battery life.