Rinse the beans and place in the crock pot.
Fill the pot with water. Cover and leave to soak overnight.
In the morning, drain the soaking water.
Add fresh water to cover the beans plus 1/2 inch.
Add 1 cup (or more) of brown sugar.
Cook on low at least 12 hours. (or high for 6-8)
Turn off heat and leave overnight.
In the morning, stir in the butter and salt.
Turn the crock pot back on warm if leaving all day/long time or low if you want to heat them up in just a few hours.
Serve warm. Freeze or refrigerate leftovers.