PURPOSE: To reduce the size of defects due to local breakage of a grid, to improve the anti-breakage and anti-corrosion characteristics, and to extend the service life, by forming recesses before expansion so that each recess contains both ends of a cut before or after cuts are formed.

CONSTITUTION: Many pressed recesses 2... are press-formed regularly at prescribed positions before cutting on a strip thin plate 1 of lead alloy comprising, for example, lead-calcium-tin alloy so that both ends of each cut are included in cuts. Then cuts 3 are provided on the thin plate 1 along lines which connect the centers of recesses 2, 2 so that both ends of each cut 3 are included in each recess 2. Then the cut 3 is elongated and opened, and transferred to expansion process. Thus the defect size of local breakage which proceeds due to the concentration of stress onto crosses of grid skeletons is reduced, the anti-break and anti-corrosion characteristics are improved and the service life of a battery can be improved.