Preheat the slow cooker if necessary; see the manufacturer's instructions. Put the apple juice, rum, honey, sugar, butter and cloves into the slow cooker pot.
Cover with the lid and cook on high for 1 hour. Reduce the heat and cook on low for 2–3 hours, or set to auto for 3–4 hours, until piping hot.
Stir, scoop out the cloves, then ladle the punch into heatproof tumblers. Decorate with slices of apple.