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Thread: Marine Battery Question

  1. #1

    Lightbulb Marine Battery Question

    I've purchased a Perko four position switch (1, 2, All, and Off), and was about ready to purchase a second battery for my boat, but the battery I was looking at was not an exact match to the one I have. I was afraid I'd fry my alternator or starter with a battery that was not an exact match.

    The battery that came with the boat is a Model 24, with 650 Marine cranking amps, 525 Cold cranking amps.

    Can I buy a battery with 600 or 700 Marine cranking amps, or do I have to have an exact match to what came with the boat?

    Sorry for the simple question. As always, thanks for the advice.

  2. #2
    Moderator AKmud's Avatar
    Join Date
    Oct 2005
    Wasilla, Alaska, United States


    It shouldn't be a problem. It is kind of like an RV charging system which charges the engine battery along with the coach batteries which are often deep cycle and much larger than the engine battery. As long as they are the same voltage you should be good to go.

    The porcupine is a peacful animal yet God still thought it necessary to give him quills....

  3. #3
    Member Roger's Avatar
    Join Date
    Apr 2006
    Sunshine Alaska


    If they are different do not switch the Perko to all and run it,That is when you might have problems frying your alternator , I have 2 different batteries on my boat and this is what I do, on the way up to where I'm going I turn the perko to one then on the way back I turn it to 2 ,That way both batteries get the same amount of charge.

  4. #4

    Default Final decision

    Thanks to AKMud, Skydiver, Snowwolfe, Paul H, DeckHand-Two, and Roger!

    I made my decision on my backup battery and went with a deep cycle marine battery which is rated the same (650 MCA/525 CCA) as my starting battery. Just like AKMud said, the voltage is the big concern. The amps just have to be big enough for the starter on the o/b. I feel safer already, having a backup battery.

    Thanks very much for your help and advice!

  5. #5
    Member Dan in Alaska's Avatar
    Join Date
    Feb 2007


    This is what I put in my boat, instead of a switch:

    Here's a simple wiring diagram decribing how I installed mine:

    A Voltage Sensing Relay (VSR) acts like an automatic switch. When the motor is running, and the starting battery reaches a full charge (13.7V), the relay closes and allows both batteries to charge. When the engine stops, and voltage on the starting battery drops to 12.8V, the relay opens and protects the starting battery from further drain. You can hear a clicking noise when the relay opens and closes, so you know for sure that it's working correctly.

    In my set-up, the only thing my starting battery operates is the outboard. Everything else runs off the house battery. Even if the house battery completely discharges, the starting battery remains fully charged to get me home.

    The beauty of a VSR is that you don't have to think about it. I does it's thing, and I don't worry about which switch position does what, remembering to flip the switch, my alternator, nothing. I have run this set-up for three years without issue, and I have never had a dead battery.

    I don't remember exactly what I paid for the VSR, but it was less than $60 shipped. I called BEP Marine and ordered it over the phone.

  6. #6

    Default Battery

    A couple things about batteries. I think most people run with both batteries on line at the same time. The problem with that is thatís only as good as the weakest battery in your system. Does not charge them both to the same level. Even brand new batteries will have a slight difference in output and capacity. Run your switch on one battery then switch to the other on ONLY WHEN ENGINE IS OFF. This way both get up to there highest potential.
    Sure there are special switchs that monitor each battery seperate, but they cost more $$
    Keep them clean, always wipe the crude that build up and dirty, any amount of dirt will start a small even if it's very small current path to ground. Cleaning is very very important! Check the water level and only use distilled water.


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