In continuing Marshal's boat owner's internet education course.....I see lots of boats that say they have "two batteries with switch".  Now I had a battery switch installed on my boat when I bought it.  It is much easier to switch the battery off when I'm not going to the lake for a few weeks instead of unhooking the cables.  Why/When is it necessary to have two batteries?  And what would be the benefit?? unless of course one battery fails.  Thanks. 

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Marshal L. McKellar
2006 202BR ALPHA I
5.0L 260HP MPI

"unless of course one battery fails" 

That's the deal Marshal.  If one fails on a boat, maybe because you spent a nice afternoon relaxing and playing the stereo, you might end up stranded if there are no other boaters around.  Or you might be one who boats offshore and a long way from land.  It's always safer if you have a back up battery, especially on the water.

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O'
"Little Mascara 3"
2003 266BR,496 MAG w/Bravo III

I agree with ol' Mike on this one.  It's just a safety/peace of mind thing.  To that end, when I'm running on the weekend, I will start out running the boat on both batteries to charge them up, and then switch over and just use one battery at a time the rest of the weekend.  All you need is a couple of hours at dinner or something when you've left your nav lights on to ruin your day if you've only got one battery.

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Todd - 4MM Gravois Arm, LoO
2000 266 BR 7.4L MPI BIII
"A-TEAM"