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Parasitic Battery Test

  1. #1
    Posting Freak
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    Oct 2007
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    Parasitic Battery Test


    I've got something that is a slow drain on my truck's battery. Day-to-day it's fine, but if it sits for 4 or 5 days the battery is dead. The battery itself, and the alternator, checked out fine. Is there a way to do this test without taking it to the dealer?

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  2. #2
    Senior Member cdseven95's Avatar
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    Mar 2009
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    503

    Re: Parasitic Battery Test

    open hood, shut door, unplug hood light if it has one.
    unbolt neg battery terminal put one probe of meter on wire, one of neg post.
    put meter on amps.
    lock door with remote if you have one.
    wait a couple minutes to see if you get a amp draw in range of what is specified for your truck

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  3. #3
    Lifer Garandman's Avatar
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    Jun 2008
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    Dorchester, MA / Mt Sunapee, NH
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    Re: Parasitic Battery Test

    Just went through this with the Triumph. They checked across each fuse. Eventually determined the grip heater relay was always on.

    An example.


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  4. #4
    Not a cool kid Charlief's Avatar
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    Aug 2007
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    Ipswich
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    Re: Parasitic Battery Test

    Do you have access to a thermal imager?

    Or find a garage that does. I deal with several that track down electrical issues using one.

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    Me no likey crash

  5. #5
    TWINS! xrocket21's Avatar
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    Central Maine
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    Re: Parasitic Battery Test

    hook a current meter in series with the positive battery terminal.
    Note value
    pull a fuse
    note value
    repeat

    Hopefully you find a fuse that makes the current drop.

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  6. #6
    Senior Member myzx6's Avatar
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    Apr 2014
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    Riviera beach fl
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    Re: Parasitic Battery Test

    Depending on what year and options your truck has, it might have to sit for a half hour or more until all the modules go to sleep and you can get a reading. Always the most suspect parts are add ons or aftermarket, like remote starters and radios and such, sometimes relays stick and alternators can go bad causing it to bleed electricity when it’s off. Anything higher then .020 A is considered a draw

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