Prepare the slow cooker with nonstick cooking spray. Place the melted butter into the bottom of the slow cooker. Add the peaches and ¼ cup sugar. Toss the peaches to coat in sugar.
In a medium bowl, whisk together the flour, baking powder, remaining sugar and cinnamon. Stir in the milk until evenly blended. Pour the batter over the peaches.
Cover the slow cooker and cook on low for 4 to 5 hours. Serve the cobbler warm with vanilla ice cream, if desired.