The present invention provides a manufacturing method for battery cells wherein an electrode assembly having an anode/membrane/cathode structure is sealed, together with an electrolyte, within a battery case made of aluminum or aluminum alloy, the method comprising the steps of: (a) forming an anodized coating on the whole surface of a battery case while forming a connection opening in the bottom surface of the battery case, for the connection of a charge pin, which is for an activation process for battery cells; (b) mounting an electrode assembly within the battery case and laser-welding a cap plate onto the top open end of the battery case; (c) injecting an electrolyte via an electrolyte injection port in the cap plate and performing the activation process for battery cells; and (d) sealing the electrolyte injection port after providing the electrolyte.