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Batteries load tested ok but voltage dropping

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Cubey, Oct 21, 2018.

  1. Cubey

    Cubey Full Access Member

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    Recently, after the truck sat for 8 or 9 days while at a campground and it was about 31 degrees (after a 22 degree low and snow) I couldn't get the truck started. The batteries went very low after only a few tries.

    Finally, I got it going with my Walmart marine battery I use for a house battery for my camper. I had both batteries tested at O'reillys in the next town (they started it the next morning at around 40 degrees out, but still seemed weak) and their tester in the back area said both were good under load.

    My alternator and voltage regulator are about a year old and are putting out proper volts, so we can rule that out.

    After sitting 4 days, I found the batteries around 12.3-12.4 before trying to start it. I will be tomorrow. I ran my generator's 5A built in dumb charger for about 5 minutes and they showed 12.8 but of course that was a float charge or whatever before they settled down.

    Sounds like I either have bad batteries, or something is pulling power while parked that didn't used to.

    Does that sound typical of dying batteries? Every other time batteries have died on me in gas vehicles, they seemed to just totally die all at once, less "kind of dead" like this. Maybe it's because if these were in a gasser, there wouldn't be symptoms yet since there's no glow plugs to strain them before cranking.
     
  2. 79jasper

    79jasper Chickenhawk

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    One could be dying.
    Could have bad cables as well. I've had a as somewhat similar instance where it ended up being bad cables/connections. So was basically running off one battery.

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  3. Cubey

    Cubey Full Access Member

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    Hmm. Well I cleaned the terminals last week so those connections should be good. I guess I will try to examine the cables when I get to a paved parking lot so I don't have to crawl around on rocks and dirt.

    But checking the voltage at the batteries themselves would show normal voltages, not severe drops, with just bad cables. The truck would see low volts, but direct readings at the batteries wouldn't.
     
  4. 79jasper

    79jasper Chickenhawk

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    I've checked voltages between the battery lug itself and the wire terminal and wire and seen differences.

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  5. Thewespaul

    Thewespaul Supporting Vendor Supporting Member

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    Any moisture or debris on the top of the battery will draw it down. You can see this by getting your meter out, putting one lead on the positive and the other on the top of the case. If it’s not clean you will usually see a voltage reading
     
  6. Macrobb

    Macrobb Full Access Member

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    Check your alternator. If it's warm after the engine has cooled off, you've got a parasitic draw. I've seen this multiple times with these trucks.
     
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  7. jwalterus

    jwalterus Made in America

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    How old are the batteries?
     
  8. Cubey

    Cubey Full Access Member

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    They are a little dirty but not horrible.

    20181021_111910.jpg


    Seems cold to me.


    I don't know. Whoever put them in didn't mark the label. I've had the truck since February 2016.

    I'm guessing their load tester gave a false reading because the batteries were topped off from the alternator right before being tested. Sitting a few days is when they seem to lose power.
     
  9. Macrobb

    Macrobb Full Access Member

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    Typically, the load testers(if it was one of those electronic ones) removes the surface charge automatically - it just drains it for like 30 seconds at a high load before testing.




    Disconect negative terminal and see what happens.
     
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  10. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    It's possible that whoever tested you batteries didn't know how to do it properly either.
     
  11. Cubey

    Cubey Full Access Member

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    It was a big automated AutoMeter machine. It was an older (but not elderly) guy. He seemed to know a fair bit about batteries, not just an untrained cashier. I suppose I can get them tested again at a different store and see if there is any difference in results. He tested both and both came up good.
     
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  12. 79jasper

    79jasper Chickenhawk

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    But were they disconnected when he tested them?
    If he didn't touch the cables, just hooked the machine up and went to testing, he's a idiot. Plain and simple.
    Look over the batteries for a sticker with a letter and number. The thing on the top is so you can punch out installation date, not manufacture date.....
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  13. Cubey

    Cubey Full Access Member

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    I carried the batteries into the store so yes they were disconnected. They were put on the fancy $3000 charger and tester they use. Something like this.

    https://www.tooltopia.com/_img/AUM/AUMFAST530.jpg

    I'll try poking around for a sticker in a few days when I'm going to be parked in one spot without moving for a few nights. That'll give me a chance to let them sit there with the negative terminals disconnected to see if they still go down below 12.6 with nothing connected.
     
  14. 79jasper

    79jasper Chickenhawk

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    Ah, I see. Had to ask, because I've seen them do that before.....

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  15. Cubey

    Cubey Full Access Member

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    That's after sitting most of the day. I did start it once a few hours before this but only idled a few minutes, I changed my mind about leaving where I was. After driving about 3 miles and sitting 10 minutes off, it shows 12.8v on the meter .
     

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