Mercury - Alternator Belt OptiMax 1.5L Series Reinforced Marine Rubber 8M0026410. Overview. If you have spent enough mornings easing away from the dock or pushing through a long run across open water, you know how much trust you put in the small pieces of your engine. An alternator belt isn't something you think about every day, but when it's doing its job, everything just feels smooth - the battery charges, the electronics stay bright, and the engine hums in that steady, familiar rhythm. That's