Drain peppers, reserving 1 tablespoon liquid; chop peppers.
Drain artichokes, reserving 2 tablespoons liquid; coarsely chop artichokes.
In a 3-qt. slow cooker combine spinach, cheeses, basil, onion, mayonnaise, garlic, artichoke hearts, and peppers.
Stir in reserved pepper and artichoke liquids. Cook, covered, on high 2 hours.
Stir dip; cook, covered, until cheese is melted, 30-60 minutes longer.
Stir before serving; serve with crackers.