To choose three different Robopon at the beginning of the game you first have to get the Secret Cave Key from Nick and the Ion Battery from the dog in one of the houses. Then, go to the back of the house where you started from. Move left until you see a door. It will now open. Go in to get two batteries. The first can be found by going up and to the right, then down to find the Moon Battery. The other one is hidden. When you enter, go straight up and it will be a dead end. Move across the right wall and you will walk through it. It may take awhile to find the entrance. When you go through the passage, you will find a chest with the Sun Battery. You can now spark the Sun and Moon Battery to get Hexbot, Spark Ion, and Moon Batteries to get Sun-Zero, or Spark Sun and Ion to get Scooter.