The Proton X (プロトンＸ?) is a treasure exclusive to the Japanese version of Pikmin 2. It is a National Hi-Top AA battery. It is found in Submerged Castle on sublevel 4, and is the equivalent of the Proton AA.
Collecting the treasure
Olimar and the Hocotate ship's notes for this treasure are the same as the ones used for the Proton AA, except in Japanese.