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The switch also alerts you to issues with your charging system if you only use one battery at a time. For instance I have twins on my boat and each motor has its own batter but it goes to switches so I can choose which battery to use for which motor. Well was doing some work in the bilge and unhooked the batterys and somehow missed putting the charging cable back on the port motor. Went out a few trips and the battery slowly drained then all of a sudden the motor started to bog down. I tried to restart but no power to turn it over. switched to other battery and it started right and up and ran fine. Point of the story is if your charging system fails and your battery dies you are dead in the water if you are on all but if you can switch to the fresh battery to get you home if you only run on one at a time.