In a small bowl, create a brisket beef rub by combining chili powder, celery seed, salt and pepper. Rub spicy mix on all sides of beef. Layer 1/2 the amount of sliced onions in the bottom of the slow cooker. Then add brisket, cutting if necessary. Layer remaining onions on top of brisket.

In a separate bowl combine hickory BBQ sauce and beer, then pour over brisket in slow cooker. Cover and cook on low for 10-12 hours, or until tender and cooked through.

Remove brisket and allow to rest on cutting board for 15 minutes. Cut brisket in half then shred beef with a fork. Turn slow cooker up to high and place shredded beef back in slow cooker with remaining sauce and stir to coat beef with sauce. Cook to ensure the beef is heated through.

Depending on the "buns" you are using: Toast buns if desired, then divide brisket onto the eight bun halves, using a slotted spoon to prevent too much sauce from making the buns soggy. Serve immediately.