an electrode body having a positive electrode and a negative electrode;

a battery case housing the electrode body;

a positive electrode-side internal terminal which is connected inside the battery case to the positive electrode and of which a part is exposed to outside of the battery case;

a positive electrode-side external terminal which is connected outside the battery case to the positive electrode-side internal terminal;

a negative electrode-side internal terminal which is connected inside the battery case to the negative electrode and of which a part is exposed to outside of the battery case; and

a negative electrode-side external terminal which is connected outside the battery case to the negative electrode-side internal terminal,

the internal terminal and the external terminal of at least one of the positive electrode side and the negative electrode side being constituted by metal materials that differ from each other,

the method comprising the steps of:

forming a terminal insertion hole in a lid of a battery case of the sealed battery;

forming a terminal insertion hole in the negative electrode-side external terminal;

inserting an upper end of the negative electrode-side internal terminal into the terminal holes so the upper end is exposed to an outside of the battery case;

deforming the upper end of the negative electrode-side internal terminal to fix the negative electrode-side internal terminal and the negative electrode-side external terminal to the lid; and

connecting the internal terminal and the external terminal to each other, wherein

the step of connecting the internal terminal and the external terminal includes:

a rough surface forming step of forming a rough surface having a plurality of recessed portions on at least one of a surface of the internal terminal and a surface of the external terminal;

a plating-joining step of arranging the internal terminal and the external terminal so that the rough surface faces another connection object with a gap between the rough surface and the connection object, forming a plated layer between the internal terminal and the external terminal, and joining the internal terminal and the external terminal to each other by causing a part of the plated layer to penetrate into the recessed portions; and

in the rough surface forming step, by performing anodization on a surface of a negative electrode-side external terminal constituted by a metal material of which a main component is Al, an alumite layer having a plurality of micropores is formed on the surface of the external terminal.