Place a heavy object on the board to keep it from sliding around on the table.

Rest the iron between the extruding battery holder tab and the corresponding solder pad to begin heating them up.

The junction will not heat up immediately. It is necessary to hold the iron in place for about 20-30 seconds before sufficiently hot.

Applying pressure to the junction, as opposed to simply laying the iron, will improve heat conductivity. This will speed up the process and result in a better solder joint.