Spray a large slow cooker (if you have two slow cookers, use both) with oil or use the liners. Sprinkle the ribs with garlic powder. Place the ribs standing up, meat side facing the walls of the cooker.
Cover and cook on low for eight hours (they can stay on warm for another three hours if you aren't home to take them out). A half hour before they are ready (7 ½ hours into the process), transfer the ribs to a platter and drain the liquid from the pot into the sink.
Place the ribs back in the slow cooker and add your BBQ sauce. Cover and cook for the last 30 minutes on low.
Place the ribs on a platter (they will be falling off the bone). Serve with extra sauce from the slow cooker on the side. Store leftovers in the refrigerator for up to four days.
In my large, oval slow cooker, I can fit one half slab of baby backs and a half slab of St. Louis ribs, cut to fit. My taller, circular slow cooker can fit a half slab of St. Louis ribs standing up.