The utility model relates to a balanced device of group battery, including little converting unit, each converting unit that declines cascades in groups, sets up bypass passage and battery charging and discharging passageway through the converting unit that declines to each, realizes that the power that the group battery fills among the the discharge process is lossless, the saving electric energy. The battery charging and discharging passageway constitutes by being used for connecting the battery port and two the at least parallelly connected charge -discharge controllable switch series connection that correspond cell, and bypass passage comprises at least two parallelly connected bypass controllable switch to the internal resistance be can reduce, heating loss and heat dissipation pressure are reduced. The device is simply reliable, at charging and discharging's in -process, makes each battery capacity who establishes ties tend to balanced, can endure the condition of power energy storage battery heavy current charge -discharge, and furthest exerts the life of the capacity of battery, extension group battery.