Metroid is the first Nintendo game using the NES-SNROM-0x PCB. The special thing about the NES-SNROM-0x PCB was that it was their battery PCB. Nintendo published five games with this PCB, and only the two first games lacked the battery (the second one was Kid Icarus).
Contributed By: Foppe
Both Metroid and Kid Icarus were released on the Famicom Disc System in Japan, which allowed the players to save their progress in three different savefiles, just like how it works in The Legend of Zelda, which got replaced by a password system when they were released in NA.
The reason they skipped the battery was to lower the production cost.
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