Join Date: Aug 2006
Location: Arlington, VA
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It would help to know a bit more about your boat: it's size, type of use, and battery charging capabilities.
I assume by "dual batteries" you mean two batteries for the house bank, and by "dual switch" you mean a common 1-2-Both-Off switch.
The preferred way to wire multiple batteries these days is to combine all house batteries into a single bank, rather than treating them as separate banks. There are several reasons for this, among them the more efficient charging potential and less wear and tear on the batteries.
The idea is that you wire all house batteries together, as a single bank. Next, you wire ALL onboard charging sources (battery charger, engine alternator, wind generator, solar panels, etc.) to the house bank, through appropriate circuit protection devices and regulating devices.
Now, you have one large house bank which is charged by a variety of sources...whatever you have available.
Then, if you have a separate starting battery, you use a device like the Xantrex EchoCharge or the Balmar DuoCharge to keep the starting battery charged. These devices are not "isolators" and they are not "combiners". Rather, they are smart switching devices which sense the voltage level on the house battery bank. Whenever that voltage exceeds about 12.8, they will recognize that something is charging the house batteries -- it doesn't matter what -- and they will bleed off a bit of current to charge the starting battery.
This works great in practice, since starting batteries typically require very little charging to keep them topped off. However, the house batteries require a lot of charging, which is why you wire all onboard charging devices to them.
Hope this helps.
Last edited by btrayfors; 01-02-2009 at 12:54 AM.