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Thread: Help with a flat start battery

  1. #1

    Help with a flat start battery

    Hi Guys

    Currently having an issue with a flat battery which has been unable to start my 50HP Honda outboard on two occasions in the Brisbane river . Both times I have had to jump start the motor using the bow AGM battery which is used exclusively for the bow electric motor. The Seamaster start battery is only 14 months old and fully recharges overnight and tests 800CCA when fully charged only to slowly discharge over a two week period despite weekly use. I have checked the instrument wiring and cannot identify any obvious electrical short in the starter circuit for the motor, although I am no expert in this field. The depth sounder, bilge pump and navigation lights run off a separate circuit from another smaller battery. No switches have been left on.

    I was wondering if the Honda analogue speedometer may be the cause. I noticed a small huntsman spider inside the casing a few weeks ago and it is now gone, presumably dead inside the unit.. Could this be causing a short as the speedo no longer works when underway? Can anyone suggest other possible causes for this problem? I am not sure how to check for any slow power draw using a multimeter and YouTube videos on the subject are not all that helpful.

    Thanks for any help in advance. SS

  2. #2

    Re: Help with a flat start battery

    Quote Originally Posted by seastrength View Post
    Hi Guys

    Currently having an issue with a flat battery which has been unable to start my 50HP Honda outboard on two occasions in the Brisbane river . Both times I have had to jump start the motor using the bow AGM battery which is used exclusively for the bow electric motor. The Seamaster start battery is only 14 months old and fully recharges overnight and tests 800CCA when fully charged only to slowly discharge over a two week period despite weekly use. I have checked the instrument wiring and cannot identify any obvious electrical short in the starter circuit for the motor, although I am no expert in this field. The depth sounder, bilge pump and navigation lights run off a separate circuit from another smaller battery. No switches have been left on.

    I was wondering if the Honda analogue speedometer may be the cause. I noticed a small huntsman spider inside the casing a few weeks ago and it is now gone, presumably dead inside the unit.. Could this be causing a short as the speedo no longer works when underway? Can anyone suggest other possible causes for this problem? I am not sure how to check for any slow power draw using a multimeter and YouTube videos on the subject are not all that helpful.

    Thanks for any help in advance. SS
    Disconnect the positive cable from the battery, you may have a engine and multiple accessories cables

    put negative lead of multimeter on battery positive terminal
    put positive cable of multimeter on the main positive feed or any others connected to the positive stud on the battery

  3. #3

    Re: Help with a flat start battery

    Quote Originally Posted by stevej View Post
    Disconnect the positive cable from the battery, you may have a engine and multiple accessories cables

    put negative lead of multimeter on battery positive terminal
    put positive cable of multimeter on the main positive feed or any others connected to the positive stud on the battery
    Thanks Steve

    I followed your advice and noted a multimeter reading of -0.01 which I assume means a 10 milliamp power draw per ? hour. Would this be enough to flatten a battery in 2 weeks? Cheers SS

  4. #4

    Re: Help with a flat start battery

    dumb question, do you have a battery isolation switch ?

  5. #5

    Re: Help with a flat start battery

    Quote Originally Posted by stevej View Post
    dumb question, do you have a battery isolation switch ?
    No, Will need to disconnect positive lead after each trip.

  6. #6

    Re: Help with a flat start battery

    1 milliamps to amps = 0.001 amps
    10 milliamps to amps = 0.01 amps
    50 milliamps to amps = 0.05 amps
    100 milliamps to amps = 0.1 amps
    200 milliamps to amps = 0.2 amps
    500 milliamps to amps = 0.5 amps
    1000 milliamps to amps = 1 amps

    my dodgy rough calcs say 1amp every 100 hours being drawn

  7. #7

    Re: Help with a flat start battery

    Quote Originally Posted by stevej View Post
    1 milliamps to amps = 0.001 amps
    10 milliamps to amps = 0.01 amps
    50 milliamps to amps = 0.05 amps
    100 milliamps to amps = 0.1 amps
    200 milliamps to amps = 0.2 amps
    500 milliamps to amps = 0.5 amps
    1000 milliamps to amps = 1 amps

    my dodgy rough calcs say 1amp every 100 hours being drawn
    So not enough to flatten the battery over a 2 week period.
    One thing I haven't worked out and it is because I am very backwards when it comes to electrickry but how did Seastrength work out the CCA of 800 amps.

  8. #8

    Re: Help with a flat start battery

    Have you got as GME radio (as in sound system rather than VHF)?

  9. #9

    Re: Help with a flat start battery

    Quote Originally Posted by Dignity View Post
    So not enough to flatten the battery over a 2 week period.
    One thing I haven't worked out and it is because I am very backwards when it comes to electrickry but how did Seastrength work out the CCA of 800 amps.
    Hi Dignity
    800 CCA is specified on the bsttery label. I assumed this means cold crankimg amps. As mentioned, I am not electrical minded so seeking advice from others with more knowledge of this issus. Cheers SS

  10. #10

    Re: Help with a flat start battery

    Quote Originally Posted by SUPERDAFF View Post
    Have you got as GME radio (as in sound system rather than VHF)?
    No GME radio or sound system on the circuit SuperDaff.

  11. #11

    Re: Help with a flat start battery

    Only takes a few really deep discharges to kill a starting battery. Charging circuit ok?

  12. #12

    Re: Help with a flat start battery

    Quote Originally Posted by Paul071978 View Post
    Only takes a few really deep discharges to kill a starting battery. Charging circuit ok?
    Hi Paul
    I use an external MinnKota battery charger to top up both batteries every 2-3 weeks. No problem until now. After speaking with EdBerg today I have decided to take this battery back to the shop and get a load test done. If it fails, a new battery may be required. Cheers SS

  13. #13

    Re: Help with a flat start battery

    Sounds to me as if there is a problem with the battery - If the battery is isolated or disconnected , the battery would only discharge ever so slightly over two weeks . You should be able to fire up a motor even 3 or 4 months down the track if the battery is isolated / disconnected .

    Chris
    Give a man a fish & he will eat for a day !
    Teach him how to fish
    & he will sit in a boat - & drink beer all day!
    TEAM MOJIKO

  14. #14

    Re: Help with a flat start battery

    Yep, I have said this many times, if you have to root around with chargers and stuff, the battery is shagged.

  15. #15

    Re: Help with a flat start battery

    Quote Originally Posted by Noelm View Post
    Yep, I have said this many times, if you have to root around with chargers and stuff, the battery is shagged.
    I thought so myself, but the battery is only 14 months old. The battery shop staff keep telling me the battery is working fine because it is becomes fully charged overnight on their charger. They maintain that it is discharging due to a circuit fault, however, I can find no reason for the discharge in the starter circuit. If it fails the load test, I will ask for a warranty replacement. Thanks everyone for their input. SS

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