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Thread: M38a1 Batteries

  1. #1
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    M38a1 Batteries

    Jeep will not turnover. Both 12 volt batteries check out at 13 v fully charged. When wired into series the combined batteries only register 16 v. Thanks for any advice.

  2. #2
    Super Moderator LarrBeard's Avatar
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    Won't Crank - Low Battery Voltage

    Quote Originally Posted by 32ACRH View Post
    Jeep will not turnover. Both 12 volt batteries check out at 13 v fully charged. When wired into series the combined batteries only register 16 v. Thanks for any advice.
    As a first step - I'd suggest taking the batteries to a auto store and have them load tested. They sound like a pair of batteries that are heavily sulfated. They show 12-volts at no load, but with even a light load, they drop 'way down- about 8-volts each.

    I am assuming you are measuring right at the battery posts, not on cable connectors. Corroded or dirty connections have happened to all of us at one time or another.

    If they drop down that far without cranking the vehicle - after a good load test - you have a pretty heavy short somewhere - I'd look at that starter switch for a problem. With that type of short, you should get a pretty good arc when you tap the cable to the battery post.

    If the batteries test OK and they drop that far down when you crank, I suspect you have a dead starter that is drawing a LOT of current or an engine that is locked up and just won't turn over. You should be able to turn the engine over with just the fan and a tight fan/generator belt. Resist the urge to put a breaker bar and socket on the crankshaft pulley - it should not take that much effort to turn it over.

    Let us know what you find - and good luck.

    (We always like pictures...)

  3. #3
    Super Moderator gmwillys's Avatar
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    Welcome 32Arch.


    First off, let's check out the resistance in the battery cables, I.e. check the connections for corrosion at the terminals. If none found, check each cable for voltage drop as a quick and dirty test, from one end to the other. On end would be at battery voltage, and so should be the other. If you want to get fancy, remove the cables and check resistance in each cable. If all is good at the cables, load test each battery to ensure you cranking amps are there besides voltage.

  4. #4
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    Battery tests passed. Posts and connectors are very clean. Reading at the starter solenoid is 16.3. Also when I connect the meter to the positive battery post and the positive to the jeep body the reading is also 16.3. Does that mean anything? Could replacing the solenoid be the fix? Thanks for helping this rookie.

  5. #5
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    Bypassed the solenoid and the starter fired right up. Will replace the solenoid. Thanks for the short detection and engine turnover tips.

  6. #6
    Super Moderator gmwillys's Avatar
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    Glad you were able to narrow it down. Don't hesitate to ask any questions you may have. We enjoy the challenges, and sharing some thoughts.

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