Laser material processing is a very rapidly advancing technology for various industrial applications, because of its many advantages. A few of its major advantages, less yet better controlled heat input, have been successfully exploited for the very critical application of aluminum alloy welding. This study suggested the source of weld-defects and its solution methods in welding a lithium ion battery with pulsed Nd:YAG laser. In the experiment, battery case has changed over joint geometry from side welding to flat welding. In the case of an electrolyte inlet seal welding, welding was carried out after pressing an Al ball and the degree of eccentricity, the contact length and the gap are presented as major parameters. With the Al ball indent improvement, the eccentricity and the gap were reduced and the contact length was increased. As a result of an experiment, a sound weld bead shape and crack-free weld bead were obtained.