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  1. #1

    Default battery question for many purposes.

    I have a 16' aluminum fishing boat with a Johnson 4 stroke 15 HP ob. This motor has an "unregulated" charger built in.

    I have run extra heavy battery cables from the motor to a single 12v Optima Blue Top battery that I have mounted in the bow of my boat (weight forward).

    I run a 12v Minnkota 45 or 50 on my bow, forward and aft fishfinders and an Eagle Intelimap GPS.

    I like the setup because I can troll with my electric for an hour or so, then fire up my ob and it charges my single battery. I like not having the extra weight/lack of space with additional batteries.

    However, on my last fishing trip, the rectifier in my ob burned up and had to be replaced. A friend told me this happened because I needed to run 2 batteries, a starting battery and a deep cycle for my trolling motor.

    Is this a correct statement?

    I like firing up the ob and having it charge my only battery. But is my built in charger being overworked? Why would it fry the rectifier? Is an unregulated charger a problem or do I need to be concerned with what I'm doing


  2. #2
    Join Date
    May 2007
    Finger Lakes, New York, USA

    Default Re: battery question for many purposes.

    First off, Welcome to the forum!!
    Your outboard is not designed to charge your deep cycle battery. First off it would take hours to fully charge a deep cycle fully. Your best bet is to have 2 batteries as your friend suggests. For your outboard get the get a starter battery for it. I would also suggest you install an onboard charger hooked up to both batteries. This will keep the deep cycle fully charged for you as well as maintain your starter battery. Once all is hooked up all you need to do when you get back is to plug in the charger and walk away. With this setup both of your batteries will aways be ready and the charger will actually help the batteries live longer.
    If you go this route you would need a 2 bank charger. Please make sure the charger handles the Optima battery. My charger I have will charge the circular style or the regualr style, but not both at the same time so you may need to buy an Optima starter battery. Feel free to PM me if I'm confusing you.
    1996 Crestliner 2160 Phantom, 1996 Evinrude 130 HP

  3. #3
    Chief Petty Officer Flargin's Avatar
    Join Date
    Aug 2008

    Default Re: battery question for many purposes.

    it is possible the regulators fried because the charging circuit was working too hard to charge the battery.

    I don't know how much charging power those smaller units are supplying.

    And yes, welcome. Great area to learn!!

  4. #4

    Default Re: battery question for many purposes.

    Thank you for the quick reply. rndn, I would agree with you that my ob charger may not charger my deep cycle, so I checked my battery to ensure that is what I have. It is actually an optima blue d34 and called a "multi-purpose" battery that can be used for a starter and deep cycle. When my rectifier burned out, my battery voltage was 10 volts. I noticed my GPS would not run on 10 volts. But I had enough cranking power to start my ob.

    I am willing to go the 2 battery route with an onboard dual battery charger. But I want to make sure I won't fry the charger on my ob again. I would prefer to place the smaller "multi-purpose" optima as my starter battery and buy a behemoth sized deep cycle for my troller.

    Do you think my multi-purpose battery voltage drain to 10 volts was enough to fry my unregulated charger on my ob?

    I read my ob manual and it says that because of the unregulated charger I should use standard lead batteries that are NOT maintenance free to avoid overcharging.

    is it this complicated? your thoughts anyone/

  5. #5
    Chief Petty Officer Flargin's Avatar
    Join Date
    Aug 2008

    Default Re: battery question for many purposes.

    It is not complicated, but you will not like to hear the answer. You have the wrong setup. Let me detail the problems:

    1. Optima's are a lot more sensitive to over charging, and unregulated charging system will overcharge or cook them. they loose life when cooked, and can blow a cap.

    2. Your 10v in the battery results in higher the drain on the charger. likely the problem of your rectifier

    3. If you don't re-charge your battery when you get home with a charger your battery is going slowly down, and down to your current 10v. Or if you have a long trip from your fishing hole to the dock, you overcharged and you fried one cell, thus your current 10v.

    I would suggest the following:

    1. Pull the battery, have someone check it (auto parts etc - you will have to leave it for them to charge it first to test it), if fried, exchange it for a new one. Keep it mounted where it is, remove from the connection from the outboard motor.

    2. buy another wet battery, or if weight is a concern, a small motorcycle battery, and install it in the back and use that to start your Outboard.

    3. Buy and install an onboard charging battery capable of charging optima's, and connect directly to the Optima.

    after a great day of catching fish, when you get home, plug in your optima, it will keep you going for years.

    You may ask why your manual say to use a wet cell battery, AGM's don't like to be overcharged. Unregulated chargers will overcharge any battery, and especially an AGM. Using a wet cell, the water will boil out, and you just replace it (which you will likely have to do)

    you can stay with a single battery, by loosing the optima, and using a deep cell - wet cell battery. But still get the onboard charger and plug it in when you get home. unless you use your trolling motor a lot, and then you will need the dual battery model.

  6. #6

    Default Re: battery question for many purposes.

    Thank you for the reply. This makes sense to me now and I feel more confident moving to a different setup.

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