I don't like beans in the slow cooker. I do a 'quick soak' with dried beans, I boil them for about 2 minutes, remove from heat and then let them soak for an hour. Then I drain them, cover them with water again and boil them (simmer) for about an hour to hour and a half.
Drain again and then add flavourings and then slow cook.
I find that beans are best baked in a dutch oven in the oven on about 300F.