Abstract: The present application relates to the technical field of lithium battery assembling, and discloses a battery and an assembling method thereof. The battery includes: a cell assembly, two ends of the cell assembly being provided with a positive electrode and a negative electrode respectively; a casing, two ends of the casing being formed as an open end and a rolled edge stop end respectively, the cell assembly extending into the casing from the open end, and the end of the cell assembly with the positive electrode being constrained and stopped at the rolled edge stop end; and a negative electrode connection piece, covering the open end, the negative electrode connection piece being a conductive piece electrically connected to the negative electrode and a casing part of the open end respectively by means of laser welding spots.