Add the ground beef and onions to a very large heavy pot or Dutch oven. Cook over medium heat, stirring and breaking up the beef, until the meat is browned and the onions are tender. Drain off the excess fat.
Drain the kidney beans, reserving the liquid. Add the reserved bean liquid, tomatoes and their juice, tomato sauce, sugar, salt and chili powder.
Break up the whole tomatoes with a wooden spoon. Bring the chili to a boil, then reduce the heat and simmer uncovered for 1 hour 15 minutes.
Stir in the drained kidney beans and simmer uncovered for 15 minutes more, stirring occasionally. Taste and adjust the seasoning before serving.
