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Can anyone recommend a book or website that could take me through the steps of a dual battery installation. Our boat currently has only one battery and we'd like to convert to a two battery system. Any help would be greatly appreciated.
 

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I have a great site booked marked someplace and as soon as I can find it, I will post it. In the meantime, trying asking the question in this forum: http://www.boatered.com/forum/
 

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It's actually quite simple. For a dual battery set up with the batteries switched (that should be how you plan to do this)

To add a second, third, fourth, etc battery to an existing circuit. Hook the batteries in parallel. Leave the negative side of your current battery connected as it is and add a cable to the negative post(s) of the new battery(ies).

For the positive side, take the positive cable off the current battery and install it on the battery switch center terminal, or output terminal. Install a new battery cable on each battery going from the positive battery post to the switch batt1 and batt2 terminals respectively. Make sure the battery switch is well over the high water mark and preferrably in a compartment other than that of the engine.

If you are unsure of the difference between series and parallel circuitry, give me a call I and I can help you.
 

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Also if its a single engine two battery setup, you'll need an isolator, to keep the batteries each properly charged. You should have a wire from the alternator to the starter or battery for charging. Mine had it on the starter, The big wire from the battery attaches to the same terminal so it charges the battery that way. Place that wire (from the alternator) on the input of the isolator. Take two new wires (minimum 10 gage) and put them on the two output terminals and one to each battery. This will keep the alternator from over charging one battery when the other is more dead. These isolators are available from boat US. They come with a wiring diagram too.
 

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A guy at Boat US told me an isolator was necessary, but I talked to a guy that works for Sunsation Powerboats and he said they are not necessary, and they don't install them. They only put the switch in. The only time both batteries are being drawn from or charged is if the battery switch is on all. If it is on batt1 or batt2, it will only draw/charge that battery, respectively. From the way the isolator hooks up, I would have to agree because it does not sound like it does anything different than the switch does(in regards to charging). If an isolator is necessary, then what is the point to having a switch? But I do not know for sure. I do not have an isolator on mine. I think I will stick a guage on it in the spring and see if both batteries are charging when I only have batt1 or batt2 on. Sure would not want to overcharge
 

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An isolator and switch are TWO TOTALLY DIFFERENT THINGS. The big advantage with an isolator is you CAN leave the switch on both and the batteries will charge correctly. Otherwise you'll have to crawl back to your switch and change it from #1 to #2 to charge each battery separately. A good practice when anchored is to put the switch on one battery only so you always have a backup.
 

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OK. Now that makes sense. The guy at boat US told me I needed an isolator even if I switched it to one battery. He claimed there was still a draw/charge to both batteries, although it was on one. I said then what would be the purpose of a switch if you can't switch it? I know they are separate things, I just meant they can are alike in that they can charge each battery separately. I don't mind switching mine back and forth. It is outside of the engine compartment and easy to get to. On my last boat I used one battery for running the engine, and one for my accessories. To avoid rewiring on this boat, I will probably use one battery all the time and just have one for a backup. Thanks for confirming how it works. I thought I was nuts
 
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