BATTERY MODULE UNIT, BATTERY MODULE, ENERGY STORAGE SYSTEM, AND ELECTRIC VEHICLE

A battery module unit including a plurality of sequentially stacked first brackets and a plurality of battery cells. Each first bracket includes a bracket body. A first battery cell group and second battery cell group disposed the opposite side of the first bracket. A connecting structure is disposed at one end of a plurality of the bracket bodies. A fastener is disposed on the first fixing bracket and is fixed to a sidewall of the connecting structure to fix the connecting structure to the first fixing bracket in a stacking direction. The first battery cell group is symmetric to the second battery cell group around a symmetric central axis of the first fixing bracket or around a symmetric central axis of a plurality of the first fixing brackets.