Mercury - Quicksilver 828507Q11 Alternator Belt Mercury 150-300HP EFI 2-Stroke Outboards 828507Q11. Overview. Your alternator belt does more than you might think - it keeps your battery charged, your electronics running, and your trip worry-free. The Quicksilver 828507Q11 Alternator Belt is the factory-fit replacement for Mercury 150-300HP EFI 2-stroke outboards, built tough to handle real marine abuse.. This belt is made from heavy-duty, fiber-reinforced rubber that won't slip or stretch under