From the Super Mario Wiki
Gameplay with two players.
Battle Course 1 is a battle course in Super Mario Kart. It seems to take place somewhere within the borders of Donut Plains. It is a square-shaped course with some multicolored walls. It has a large open place in the middle, where players are more likely to be hit with an item. The aim is to hit the opponent three times with items to get rid of the three balloons around each player.
Unused minimap of Battle Course 1
from Super Circuit
Although they didn't appear in Mario Kart: Super Circuit, tilemaps and minimaps exist for all four of the Battle Courses from Super Mario Kart. These could have been used as placeholders before the new ones were completed, or it may have been possible to unlock these courses like the tracks at one point. Unlike all other tracks and battle courses in the game, which are stored in chunks, these are each stored in one piece, as in Super Mario Kart.