Grease your slow cooker really well.
Spread apple pie filling on the bottom.
Sprinkle cranberries over the apple pie filling.
Sprinkle cake mix evenly over the cranberries.
Top the cake mix with a layer of butter slices.
Cook on low for about 3 1/2 to 4 hours. (depending on your slow cooker, it may need more or less time so keep an eye on it).