Add all the ingredients along with ¼ tsp salt and ¼ tsp pepper into a large slow cooker and stir to combine.
Cover and cook on low for about 8 hours.
Drain the beans, reserving any liquid.
Add the drained beans to a large bowl and mash with a potato masher, adding the reserved liquid a little at a time until desired consistency.
Add additional salt and pepper to taste.
