A parallel device for a battery module and controlling method thereof

A parallel device for a battery module including a plurality of battery groups, comprising: a plurality of switching units, each comprising a first switch and a load and each connected with a battery group to form a braches which are connected together in parallel; and a controlling module, connected with the first switch and the battery group and configured to collect a voltage of the battery groups, calculate the voltage differences between the voltages of the battery group, compare the voltage differences with a voltage reference and control the first switch to open or close according to the voltage comparison result. A controlling method of the parallel device for a battery module including a plurality of battery groups is also provided.