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. At least one battery cell on one side of a first fixing bracket forms a first battery cell group. At least one battery cell on the other side of the first fixing bracket forms a second battery cell group. The battery module unit further includes a first connecting structure, disposed at one end of a plurality of the bracket bodies. A fastener is disposed on the first fixing bracket. The fastener is fixed to a sidewall of the first connecting structure so that the first connecting structure is fixed to the first fixing bracket in a first direction. The first direction is a stacking direction of the plurality of first brackets.