Place the beans, onion half, bay leaf, garlic, 2 to 3 teaspoons kosher salt (I always use 3), pepper flakes (start with ½ teaspoon if you are sensitive to heat), and olive oil (if using) into a slow cooker.
Cover with 8 cups of water.
Cover pot.
Cook on high heat for 6 to 8 hours or until the beans are done, but start checking at the 4-hour mark — all slow cookers are different and times might vary, too, depending on the age of your beans.
Taste. Add more salt to taste ½ teaspoon at a time.
Note: The beans develop more flavor as they cool in their cooking liquid, which will continue to season them.
Store the beans in their cooking liquid.
