Mercury - Quicksilver 828507Q4 Alternator Belt Mercury 2.5L V6 OptiMax Outboards (Non-Pro Models) 828507Q4. Overview. A good alternator belt keeps your outboard's electrical system steady and dependable. The Quicksilver 828507Q4 Alternator Belt is the same factory-installed part Mercury uses on 2.5L V6 OptiMax outboards (non-Pro models), serial number 1B227000 and above.. If your old belt is worn, squealing, or slipping, this OEM replacement restores proper alternator performance and power deliv