Microwave onion, garlic, and oil in bowl, stirring occasionally, until onion is softened, about 5 minutes. Transfer to slow cooker.
Stir water, beans, ½ cup barbecue sauce, coffee, sugar, and bacon slices into slow cooker. Cover and cook until beans are tender, 9-11 hours on low, or 5-7 on high.
Discard bacon slices. Stir in remaining 2 tbs barbecue sauce and mustard and let sit until thickened slightly, about 10 minutes. Season with salt, pepper, and hot sauce to taste and serve. This dish can be held on warm setting for 1 to 3 hours before serving. Loosen with additional hot was as needed before serving.