Welcome to the forum. You will find plenty of interesting information and helpful people here. Well worth spending some evenings in front of the TV browsing through previous topics. Most are still current, and many apply to more than one model of boat, as they all have similar systems.
And while you are there, how about going to the introductions board and tell us which boat you have and which waters you call home.
I would need a few more words around your question to help me understand the specific problem. Are you talking about the reverse polarity indicator? Or the DC side of things? Then I am sure you will get several helpful replies.
Welcome to the forum. Could you provide some more detail regarding your question? Is the battery charger the power supply you are referring to? What polarity are you referring to? Is it a reverse of the battery cables or is it a reverse of the mains input polarity?