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Batteries Draining Quickly - Check Alternator?

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  • Batteries Draining Quickly - Check Alternator?

    I have a two battery setup with a Perko switch. My usual operation is to use battery 1 for normal cruising, then switch to battery 2 when anchored. Recently my cranking battery (#1) has been draining very quickly to the point that voltage alarm goes off. I switch to deep cycle (#2) and then it drains quickly.

    Battery #1 is brand new (Deka Dual Purpose) and Battery #2 (Interstate Deep Cycle) is less than 2 years old.

    I've never had a problem with #2 and have not had #1 for very long, but made sure it was topped off before connecting.

    Alternator is the original.

    This year is the first time I've stored my boat in dry stack storage, so I don't have the option of using my on-board battery maintainer when not in use.

    Any thoughts?

  • #2
    could be rectifier - disconnect battery from alternator - see if it continues to drain. happened with my 1995 205
    sigpic...A bad day water skiing still beats a good day at work...1995 Pro Star 205....


    • #3
      Mikeg205, thanks for the response. Is the rectifier built into the alternator? If I need to replace one or the other where do you recommend finding parts quickly, and do you recommend getting a higher amp rating than the original? Thanks!


      • #4
        Check the voltage at the alternator to block ground point and check the voltage across the battery, Figures should broadly be the same.
        With the engine running you should also check for a voltage between the alternator +ve and battery +ve. Likewise check for a voltage between the battery -ve and grounding point on the engine. This will tell you if you have any losses. Any more than 0.5V, start hunting for a loose or corroded connection/bad ground etc.

        I recently chased down a problem with my "alternator" as my batteries weren't charging properly, it turned out to be the 50A circuit breaker was corroded on the inside thus causing a significant voltage drop and messing with everything else. A simple fix and whilst I was at it I reconfigured some wiring to allow for an increased alternator in the future, and I'm back in business.


        • #5
          The simplest answer would be a bad battery... I would start there. Swap the battery for one that you know is good and see what happens...

          I bought a used car for my teen recently and the battery would go dead overnight. The tester at the parts store read it as a "good" battery. Not the case, bought a new one and all has been good...


          • #6
            Recharge the batteries, put the engine on a water supply and test the alternators output with a basic digital voltmeter, from the alternator to the batteries. You could have a bad alternator or a bad cable thats preventing the batteries from the being replenished.