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Old 05-03-2010, 12:21 PM   #385
Grady223
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Quote:
Originally Posted by jrc View Post
A lot of boats only charge the battery that is on. So if you put the switch to "1" then battery #1 starts the boat, runs the engine and is charged by the alternator. In this case battery #2 in not used but also not being charged.

If you switch to "2" it's exactly the opposite. So if stop at the sandbar and run your radio all day and kill one battery the other will get you home.

Now if you get to the boat and batteries are a little weak from sitting too long, you can select "both" to get more cranking current and start the boat. You can also leave it on "both" to charge both batteries. But if you forget and leave it on "both" and go to the sandbar, run your radio, you drain both batteries. If you use enough current you could be stranded.

When I had this setup, I used "1" on Saturday and "2" on Sunday. That way both batteries got a charge every weekend and I avoided the risky "both"

Finally don't use "off" while the engine is running, on most boats it will instantly fry the alternator diodes and a possibly damage your electronics like stereos and GPS.
And, don't leave it set to both, neither will charge and you could damage the alternator
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