I've been kicking around the idea of adding a house battery to my boat to handle the electonic fish finder, a couple LED lights, radio, nav lights, bilge pump and a couple of outlets for USB support (like charging phones, etc.). Currently these items are running off the cranking battery, not ideal. I don't care for this setup and want to put these items on a seperate battery so as not to run down the cranking battery, thus avoid a self induced headache. I can transfer the leads to the new battery and leave the cranking battery as a stand alone battery. When the boat is in storage for winter I can charge these two batteries with a two bank charger. I'm thinking that there should be a simple way to charge both batteries when the motor is running. My question is what is the simplest way to accomplish this?