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Thread: Alternator or Battery??

  1. #1

    Default Alternator or Battery??

    So Vivid (2002 Miata) has been "resting" for an extended period.

    Back in May, I got it a new Battery.

    She was dead as a Mackerel Sunday but if I charged it up and got it to start.

    No dash lights at all, but a quick check with the meter was showing the alternator was cranking out about 16V..........

    I'm no rocket surgeon but I'm thinking 16 volts is a bit high.. But who is to blame? Battery or the Alternator or both??

    TIA

  2. #2
    Mr Miata Solutions Rogue's Avatar
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    Slow charge the battery and recheck. You do have a AGM battery right?
    They sure hate to be discharged, get a battery tender.
    Battery's sure are not what they used to be.

  3. #3
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    It's probably your free Harbor Freight multimeter!

  4. #4

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    My Vivid's battery had an "extended vacation" last year too. I put it on a smart charger set to "AGM" and it would take a charge for just a bit and then the charger would determine that the battery was kaput and shut off. I started again the next day with the same end result. I kept at it for a few days before the battery was alive enough so the charger would recognize it and complete the cycle. Now, all is well with no problems since.

  5. #5

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    Quote Originally Posted by Rogue View Post
    Slow charge the battery and recheck. You do have a AGM battery right?
    They sure hate to be discharged, get a battery tender.
    Battery's sure are not what they used to be.
    Yep AGM. I got a MAZDA Miata Battery Deka/East Penn 8AMU1R AGM t0 be specific.

    Thought those were the good ones.

    Quote Originally Posted by sammm View Post
    It's probably your free Harbor Freight multimeter!
    I tried a coupe of them on it thinking it was the meter.

    Also my OBD Software was reporting a 15+ voltage.

    Quote Originally Posted by cwisenheimer View Post
    My Vivid's battery had an "extended vacation" last year too. I put it on a smart charger set to "AGM" and it would take a charge for just a bit and then the charger would determine that the battery was kaput and shut off. I started again the next day with the same end result. I kept at it for a few days before the battery was alive enough so the charger would recognize it and complete the cycle. Now, all is well with no problems since.
    Swiped my Harley Neighbor's fancy AGM charger and it has been passing the tests and charging.

    But If I leave the car it drops back to 10.4V per the chargers built-in meter..... I haven't kept track of how long it takes to go back to 10.4 but it directly corilates to when I want to use the car.

    Now that it has cooled off I need to pull the battery and see what it does independent of the car. Just find it hard to believe my new battery is a

  6. #6

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    I buy my Miata batteries through O'Reilly's. Mostly out of convenience but also because they have a generous free replacement warranty (I think it's 2 years). I also use a Schumacher on board battery tender on each of my Miatas. Haven't had a dead battery since as long I remember to leave it plugged in when not in use.

    BTW, Hi everybody!
    ...and across the line.

    1996 Mazda Miata - R-Package (Eve-L)
    2012 Mazda CX-9 - Grand Touring (Dory)




  7. #7

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    Quote Originally Posted by Rogue View Post
    get a battery tender.
    +1 for this. Went through a battery in the Miata because it just sat. I got a Battery Tender, so far no issues after a couple years. Also +1 for O'Reilly battery. They make it easy, the part number is "MIATA".
    "Racing makes heroin addiction look like a vague longing for something salty" - Peter Egan

  8. #8

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    Harley Neighbor "Niuked" the battery with his fancy charger so far so good, but I have been running the car every other day. Got a feeling when it sits for more than a couple of days the dead battery problem will more than likely return.

    What is the "normal" parasitic draw on an NB Miata? Figure something may be staying on that should be off when the car is resting.

  9. #9

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    Disregard earlier post -

    Eye Dr. Appointment today.

    1. Miata Started up great in the Garage this morning after sitting since Saturday.
    2. Then it Fired up great at the Eye Dr.'s office (about 2 miles from the house).
    3. Then it wouldn't start at the gas station.......(Across the street from the eye Dr.)



    All within an hour.

    Going to go get it another Battery later today.....

  10. #10
    Mr Miata Solutions Rogue's Avatar
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    Part Number #MIATA

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