Lightly grease the inside of a 6-quart slow cooker, preferably an oval model. Place a round of parchment in the bottom and grease it lightly for easier removal.

Pour the melted butter over the bottom of the slow cooker and sprinkle the packed brown sugar evenly over it. Arrange the drained pineapple rings over the sugar, placing one maraschino cherry in the center of each ring.

If needed, cut extra pineapple rings in half and use the pieces to fill open spaces. In a bowl, combine the cake mix, eggs, oil, and one cup of pineapple juice mixed with water.

Beat the batter just until smooth, generally 1 to 2 minutes, and do not overmix. Gently pour it over the pineapple layer, then spread it evenly without disturbing the fruit.

Cover the slow cooker and cook on HIGH for 2 to 2 1/2 hours. For a less-wet surface, place a clean kitchen towel beneath the lid, keeping it away from the heating element and preventing it from hanging down the sides.

Begin checking near the early end of the cooking range because slow cookers vary. The cake is ready when the center is set and a toothpick inserted into the cake comes out with only a few moist crumbs.

Turn off the slow cooker and let the cake stand for 10 to 15 minutes. Run a knife around the edge, place a serving plate over the crock, and carefully invert the cake onto the plate.