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Thread: Dead battery

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  1. #1
    Obi Wan
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    Dead battery

    The Alfa was entered in a club concours this afternoon. I put in a new battery about 6 weeks ago. Seemed to be charging fine. Last drove the car about ten days ago. Went to Vermont this past weekend and disconnected the battery with that little green knob "just in case". Tried to start it and cranked slowly for 5-6 seconds and died. Dead battery. BTW, when we go to Florida, both the TR6 and the '02 Honda with a 6-year old battery sit in the garage with their batteries hooked up and have never failed to start almost instantly after sitting for 3 1/2 months. Question - how can a new battery go dead with its ground terminal disconnected? Is this a bad battery? How can I tell? It has checked out on a VOM and so has the alternator. I'll have to check it again tomorrow when my 6-amp charger is through charging. Any theories?

  2. #2
    Luke Skywalker LarryK's Avatar
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    Re: Dead battery

    Do a load test. If not holding a load will leak down sitting.
    Larry K
    58 Jag 3.4 MK 1 auto under restoration, 57 Jag 3.4 MK1 manual ,
    03 Cooper S, 2011 Cooper S Countryman, 2011 Land Rover LR4 HSE LUX, 1964 Valiant V200
    Also had , 68 Cortina 1600E, 64 Spit 4 & 80 1500, 73 GT6 3, 71 XJ6, 79 XJ6, 86 XJS V-12, 53 XK120 OTS.

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    Darth Vader
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    Re: Dead battery

    New as in New from the Store?
    It should hold a charge for a long time if it is disconnected. I presume you have checked that your Green knob is actually disconnecting the battery?

    David
    TR3A TS75524L

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    Yoda Gliderman8's Avatar
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    Re: Dead battery

    Quote Originally Posted by DavidApp View Post
    New as in New from the Store?
    It should hold a charge for a long time if it is disconnected. I presume you have checked that your Green knob is actually disconnecting the battery?

    David
    I agree. Grab your VOM and check the continuity of the green switch to see if it actually disconnects.
    Elliot
    Central PA
    1973 TR6 Damson Plum / Biscuit interior, HVDA 5-speed, Good Parts Hubs
    1976 TR6 White/Biscuit interior SOLD
    Nostalgia isn't what it used to be.

  5. #5
    Great Pumpkin TR3driver's Avatar
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    Re: Dead battery

    I bumped into this on a Spitfire, might be worth looking at. "Green knob" worked fine with hood up; but was just enough taller than a standard battery clamp that the hood put pressure on it when closed. Just enough to make the "switch" still conduct a little bit.

    At least part of the "leak" turned out to be an aftermarket stereo, that drew around 30ma all the time. Probably to keep the preset memory alive.
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
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  6. #6
    Obi Wan
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    Re: Dead battery

    Ok - I think I discovered the source of the short circuit by accident, and when I discovered it, I burst out laughing at how simple and stupid it was. I discovered it by using my Radio Shack multimeter, starting at the battery itself. It was fixed with a 13 mm wrench. See who can guess it.

  7. #7
    Yoda Gliderman8's Avatar
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    Re: Dead battery

    Was the battery hold-down bracket making contact with the switch or post of the battery?
    Elliot
    Central PA
    1973 TR6 Damson Plum / Biscuit interior, HVDA 5-speed, Good Parts Hubs
    1976 TR6 White/Biscuit interior SOLD
    Nostalgia isn't what it used to be.

  8. #8
    Great Pumpkin TR3driver's Avatar
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    Re: Dead battery

    Loose clamp?
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Yoda TOC's Avatar
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    Re: Dead battery

    Ah. The famous 13mm wrench trick. Easily overcome with an SAE 1/2" wrench.

  10. #10
    Obi Wan
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    Re: Dead battery

    Elliot guessed it. He wins the prize. The ground cable clamp was (barely) touching the battery hold-down rod. Not wanting to bend the cable, I had kept it straight and tightened it up not realizing that the end of the clamp was making contact with the bolt because it was hidden underneath. I discovered it quite by accident. Touching the painted battery frame gave zero reading, but the two nuts on the end of the bolt gave me 12.7 volts. I loosened the clamp, rotated it slightly and re-tightened. Now we'll see if that was it or are there more gremlins lurking.

  11. #11
    Yoda Gliderman8's Avatar
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    Re: Dead battery

    Thanks for the update. Let me know if you want my bank routing numbers
    Elliot
    Central PA
    1973 TR6 Damson Plum / Biscuit interior, HVDA 5-speed, Good Parts Hubs
    1976 TR6 White/Biscuit interior SOLD
    Nostalgia isn't what it used to be.

  12. #12
    Obi Wan
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    Re: Dead battery

    Further update. Even with the green knob turned all the way out - which is unnecessary - I still get a .02 volts reading when touching the green knob or the holddown bolt. It should read zero volts, no? I'll check it against the TR6 and the Subaru and see what it shows.

  13. #13
    Great Pumpkin TR3driver's Avatar
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    Re: Dead battery

    Digital meters will often give a voltage reading when connected to nothing at all. Seems like they manage to pick up and rectify random radio waves or something.

    Had an experience with that just today; cheap HF DMM is apparently picking up ignition noise from my old 2 cylinder tractor and displaying it as DC voltage. It reads all kinds of crazy voltage, even with the leads shorted together! Hmm, 600 volts across a dead short and it's not even warm. Something wrong with this picture
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

  14. #14
    Yoda TOC's Avatar
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    Re: Dead battery

    That's why my VOM's are analog. Simpson 260 and Tripplett 630.

    Wait until you run into an old battery that has a case failing.....and you get bleed through of voltage with even one cable disconnected.

  15. #15
    Obi Wan
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    Re: Dead battery

    Re-checked. Voltage now 0.00. It bleeds off slowly. But battery voltage across the terminals has dropped from 12.6 to 12.45 just sitting with green knob loosened. I'll check it again tomorrow.

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