BATTERY -- Starting/Trolling

Discussion in 'OnBoard Electronics & Controls' started by MercMan69, Apr 2, 2007.

  1. MercMan69
    Joined: Apr 2007
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    Location: House Boat

    MercMan69 Junior Member

    I am currently using a marine deep cycle battery for starting my old 1969 merc 650, 65 hp outboard. I am looking into buying a trolling motor, and i am wondering if the deep cycle battery will start the outboard AND run the trolling motor. Does the outboard charge the battery? Any help??
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    A deep cycle battery is intended to run continuous draw devices (like trolling motors) and though they can start your outboard, aren't at their best doing so.

    A starting battery (like used in your car) is designed for a fast, heavy draw, then gets quickly charged back up, usually by an alternator.

    They also have been selling starting/deep cycle batteries in recent years. I suspect these are just smaller plate deep cycle batteries, made to fit a market need or just a marketing ploy to sell more batteries (most likely).

    If you use a trolling motor a lot, like fishing your favorite honey hole, then you can easily drain down the battery enough so that it will not start up your outboard. This is why most serious fisherman use a duel battery setup, one for starting the outboard and the other for puttering around on the trolling motor.

    Twin batteries are simple enough to arrange, requiring as little as a switch to separate the two. This permits you to troll you brains out, even running it good and flat, then switching to your starting battery so you can crank up the old girl and go home. You don't even need the switch. You could just have two batteries, one for the outboard and the other for the trolling motor, but this would mean you wouldn't easily be able to charge up the dead one with the outboard. This is where the switch comes in real handy.

    Lets say you're over the mother load of fish and are down to your last beer (damn). You've been hanging over this monster load for several hours and don't want to give up, but the trolling battery is getting real weak and you need beer too. You can crank up the engine (starts with the dedicated engine battery) blast over to the local bait and beer store on the near by shore, load up on essentials (like beer), all the while charging up the trolling battery. The switch will also permit you to use both batteries at once, which can be handy if you've drained down both to some degree and nether will start the boat alone, but together they will. Pretty slick right. Most every marina or boat part store (West Marine, etc.) will have these switches and they don't cost too much. The instructions are a walk in the park, so you can install it in an hour, with the hardest part being where to mount the darn thing. You'll need some battery cable and ends crimped on, but most marinas can do this pretty cheap (I think West Marine will too) and it ain't so difficult that you couldn't figure it out and do it your self.

    And yes, assuming your charging system is up to snuff, the outboard should charge the battery (or two).
  3. charmc
    Joined: Jan 2007
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    Location: FL, USA

    charmc Senior Member

    Basically, I'm going to reinforce everything PAR said. The cost of a starter battery for your 65 hp motor is not that much, and the security of knowing that, no matter how much you draw down your trolling motor battery, you can start the main motor.....that's priceless. The switch PAR mentioned is a great convenience. Just be sure the word "isolator" or "isolation" is somewhere in the description of the switch. The isolator functions like an electrical one way road, preventing the battery with less power from drawing down the fully charged one. You can switch to using both batteries if you need to, but otherwise they are fully isolated from each other, even though both can be charged. I did my first rig on a small cruiser, too small for a generator. We would go to a secluded cove, anchor out for 2-4 days, running radio, tv (for the kids), lights, etc., knowing the starter battery was always fully charged and ready to go. Installation was very easy.

    Your charging system should have no trouble handling 2 batteries, and the improvement in the quality of your boating/fishing experience will be great. I'd say go for it.

  4. Ike
    Joined: Apr 2006
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    Location: Washington

    Ike Senior Member

    I echo both of them. The plates in a deep cycle battery are much thicker than in a starting battery. They are made to release current slowly for a long time. Starter batteries have thin plates made to discharge a large current for a short period of time. Constantly using a deep cycle for starting can actually warp the plates (overheating) and then they make contact and short out.

    Read this a section on batteries on my web site.
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