Can a dirty battery create problems on my boat?
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Dusty, dirty batteries can cause accelerated self discharge.
The battery you see in the photo above is somewhat vulnerable to accelerated self-discharge if the dust and sawdust you can see on it’s top surface gets moist. In a general sense today, new batteries are far less susceptible to self-discharge, especially via their case tops. This all has a lot to do with the case materials being made of smooth, plastic materials versus gooey tar like materials and bakelite of old.
The issue here is that any dirt particles that end up on the top surface of the battery become a medium for moisture droplets to adhere to. Enough of them and you can create a conductive electrical pathway from one battery post to the other, or down the side of the battery case. This alternate path for electrical current flow will allow the battery to slowly discharge itself, all very quietly and without incident, other than a dead bettery.
The bottom line here is to keep the battery case surface clean and free of dust and engine room grime. Its a subtle point, but it will enhance battery life. Just use warm water and a little baking soda to get that battery top sparkling clean.