Thread: Battery Drain

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  1. #1
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    Battery Drain

    I have a Mercury 2016 150Hp outboard SN 2B202320. The battery went dead. I charged it up and put an amp meter between the post and the negative lead. it was drawing 2.5 amps. When I disconnected the 2 wire lead to the alternator the draw went away. I connected the battery and put the meter between each of the pins and their corresponding contacts and saw no current draw. I then checked the voltage on the contacts there was battery voltage on one. I turned on the key and saw battery voltage on both. I removed power cable from the alternator and did a continuity check between each of the 2 pins and the terminal of the alternator to ground. There was no continuity. I connected everything up and ran the engine at 2000 RPMs and I read 14.5 volts. So I am having trouble believing the alternator is bad. Does anyone have any suggestions on what else I can check? Any guidance would be greatly appreciated. Thank you.

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    #2
    Did you measure AC Voltage across the battery terminals w/ the engine running? If not 0 or real close, could have bad diode in the rectifier.
    2016 Ranger 1850 LS Reata / Merc 150 4s / SmartCraft / Lowrance HDS Carbon SS3D

  3. Member
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    #3
    I would like to help but to do so I would need to understand the problem exactly;

    did the battery go dead while the boat is sitting in the driveway or did it die while you were using the boat?

    this is to determine if a load drained it (like a short or faulty accessory switch ) or if its because it is not getting charged as MichalJ3 was saying...

    how old I the battery ? 1000 CCA ?

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    #4
    It dies while sitting overnight. I purchased a new battery and charged it fully. before taking measurements.

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    #5
    I checked the AC voltage this weekend. At 2000 rpm I read between 85 and 90 mV. Not sure if that is normal.

  6. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #6
    Make certain that you have turned the key OFF before retesting for that 2+ amp draw you recorded earlier. Make sure that ONLY the engine cables are connected.

    This should be done after running the engine, and then turning the key to the OFF position (so that the Voltage Regulator had been "live").

    Other tests are normal... except for the 2+ amp draw you described (provided that indeed the key was OFF).


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor

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    #7
    Yes the key is off for all the tests. except of course the AC voltage test. Could the voltage regulator or the diode tree be causing this draw. or could it be the main power relay or something further down the line?

  8. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #8
    I suspect it is the voltage regulator in the alternator. If you can unplug the SMALL plug from the alternator, and ELIMINATE the drain entirely (repeat the test to confirm), it is VERY likely that the alternator is the problem.

    Another simple method: Disconnect alternator only, fully charged battery, then check battery the next morning. Battery good = Alternator likely the problem.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor

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    #9
    Thank you. I will get another one when available and let you know.

  10. Member
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    #10
    Replacing the alternator fixed it. I no longer have a current draw. In fact the alternator puts out 14.5V at idle. Thank you all for your assistance.