A battery module, comprising: a plurality of battery cells ; a housing , wherein the housing comprises an inner cavity for accommodating the battery cells ; an output assembly , wherein the output assembly is electrically connected to the battery cells , and the output assembly is arranged at an outer side of the housing that faces away from the battery cells ; and a module upper cover of a plate structure overall, wherein the module upper cover seals the inner cavity, and the module upper cover comprises a body and an extension , wherein the extension is connected to the output assembly ; wherein the extension extends from one side or two sides of the body along a length direction (L) of the battery module; wherein the output assembly comprises a sampling output base , and the extension comprises a first extension , wherein the first extension is connected to the sampling output base , and wherein either (i) the first extension is provided with a groove along a width direction (W) of the battery module, and the sampling output base is provided with a first engaging portion , wherein the first engaging portion cooperates with the groove ; or (ii) the first extension extends downward along a height direction (H) of the battery module to provide a connection plate , the connection plate being provided with a through hole , and the sampling output base is provided with a first protrusion on a side facing toward the connection plate , wherein the first protrusion fits with the through hole . a plurality of battery cells ; a housing , wherein the housing comprises an inner cavity for accommodating the battery cells ; an output assembly , wherein the output assembly is electrically connected to the battery cells , and the output assembly is arranged at an outer side of the housing that faces away from the battery cells ; and a module upper cover of a plate structure overall, wherein the module upper cover seals the inner cavity, and the module upper cover comprises a body and an extension , wherein the extension is connected to the output assembly ; wherein the extension extends from one side or two sides of the body along a length direction (L) of the battery module; wherein the output assembly comprises a sampling output base , and the extension comprises a first extension , wherein the first extension is connected to the sampling output base , and wherein either (i) the first extension is provided with a groove along a width direction (W) of the battery module, and the sampling output base is provided with a first engaging portion , wherein the first engaging portion cooperates with the groove ; or (ii) the first extension extends downward along a height direction (H) of the battery module to provide a connection plate , the connection plate being provided with a through hole , and the sampling output base is provided with a first protrusion on a side facing toward the connection plate , wherein the first protrusion fits with the through hole . (i) the first extension is provided with a groove along a width direction (W) of the battery module, and the sampling output base is provided with a first engaging portion , wherein the first engaging portion cooperates with the groove ; or (ii) the first extension extends downward along a height direction (H) of the battery module to provide a connection plate , the connection plate being provided with a through hole , and the sampling output base is provided with a first protrusion on a side facing toward the connection plate , wherein the first protrusion fits with the through hole . <EOS>