The invention discloses a connecting device and a battery module. The connecting device comprises: a battery connecting piece; two wings of the battery connecting piece are welding areas; The invention also comprises a pair of module connecting pieces, one side of the module connecting pieces is a welding area and the other side is a bolt connecting area, and the bolt connecting areas of the two module connecting pieces are overlapped and bolted to be fixed. The invention synthesizes the advantages of two connection modes of welding and bolt connection, ensures the reliability and stability ofbattery connection, and improves the flexibility of module connection collocation and assembly efficiency.