Soak the beans overnight, changing water several times. Put beans in crock-pot and cover with an inch or so of water. Add salt, onion, garlic, and chili powder. Cook on low until beans are soft (about 18 hours? I forget). When beans are cooked, ladle off and reserve some of the liquid from the top. Mash the beans well. (I never do this as well as I'd like; I've tried a potato masher and an empty iced-tea jar.) Add reserved liquid as necessary for consistency. (I never have to add any, myself.) Stir in the chopped chiles and the salsa; heat through.