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https://www.boards.ie/discussion/2055940817/signature-rules

Can a bad alternator drain the battery when the car is shut off?

2

Comments

  • #32
    Hellrazer
    Moderators, Arts Moderators, Recreation & Hobbies Moderators Posts: 10,700 Mod ✭✭✭✭Hellrazer


    Your new battery is fecked if its dropping to 7v over night.

    For a car battery to loose that overnight you`d have to have something quite power hungry causing the drain and an alternator wouldnt be where Id start - I dont remember ever seeing a faulty alternator drain a battery.

    My opinion - theres a dead cell or cells in the new battery - not that unusual especially if the battery was sitting on a cold concrete floor in the factors. . You say it was ok up until 10 days ago?

    Probably the start of the colder nights and thats whats killing it.

    Id get a multimeter and see what its charging at - should be around 13.5 - 14 volts.

    If its charging at that then the alternator is good.

    Then check the battery for voltage - usually around 12.5 is fine. Leave it overnight and check in the morning - it should really only lose around 1 volt. Any more than that Id charge it up again and the next night disconnect the red battery cable and check it the next morning. If it loses more than 1 volt again its 100% the battery.



  • #33
    Igotadose
    Registered Users, Registered Users 2 Posts: 13,708 ✭✭✭✭Igotadose


    So, after 2 weeks of investigation, all that was found, was a fault logged by the computer about the control box next to the battery. The mechanic wasn't sure it would fix the problem and advised us to take it home and wait and see. He had tested the battery each morning and looked for parasitic devices and tested the alternator, nothing. I'm confident he tested everything he's quite savvy about car electrical systems. This isn't the dealership who had no clue and lots of attitude.

    I've since acquired a 'jump charger' box that should bail me out should the battery go dead again. Nifty thing, charges on USB and includes a torch.

    In the last 10 days or so, the car has started fine every morning. We picked up the car on Tuesday, it was fine.

    Wednesday morning, the key fobs again stopped working. This is what happened when this saga began, the key fobs stopped working a few days before the battery died.

    Should we replace the control box? Could that be causing the problem? The mechanic said we didn't need a new battery, so at this point, I think I'm going to let it go and see what happens.



  • #34
    mickdw
    Registered Users, Registered Users 2 Posts: 23,406 ✭✭✭✭mickdw


    So your main dealer diagnosed alternator.

    Your expert auto electrician diagnosed feck all and now you are no further along other than deciding to carry a jumpstarter.

    Main dealer as stupid as they can be would clearly have read the same fault your guy did. They may however have seen the issue 100 times before and know that fault at control box is result of alternator issue or may have factory technical data directing them that way.

    I have seen alternator causing this kind of issue.



  • #35
    FREDNISMO
    Registered Users Posts: 339 ✭✭FREDNISMO


    Had a similar problem on my car, turned out to be a short on starter motor that was draining battery overnight, new starter motor no problems since, took a while to find problem.



  • #36
    Igotadose
    Registered Users, Registered Users 2 Posts: 13,708 ✭✭✭✭Igotadose


    Well, it's died again. Seriously thinking of scrapping it at this point; an alternator, a new battery and a control box is a bit much to spend right now. Will try jump starting tomorrow.

    Sure does seem like the cold weather here is part of the problem; when the car was at the mechanic(s) it never failed to start, but it was stored indoors or was out in warmer weather than we've had here the last few days.



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  • #37
    mk7r
    Registered Users, Registered Users 2 Posts: 777 ✭✭✭mk7r


    https://www.boards.ie/discussion/comment/121453464#Comment_121453464

    This really points towards the battery itself, not a drain on the battery.



  • #38
    Igotadose
    Registered Users, Registered Users 2 Posts: 13,708 ✭✭✭✭Igotadose


    https://www.boards.ie/discussion/comment/121453741#Comment_121453741

    Hmm. Battery just measured 7.6V. I plan to measure & boost it tomorrow and drive it around - don't feel it would be wise to drive it around tonight with weird problems occurring.



  • #39
    mickdw
    Registered Users, Registered Users 2 Posts: 23,406 ✭✭✭✭mickdw


    https://www.boards.ie/discussion/comment/121453741#Comment_121453741

    It sure does.



  • #40
    The Continental Op
    Registered Users, Registered Users 2 Posts: 6,978 ✭✭✭The Continental Op


    https://www.boards.ie/discussion/comment/121453752#Comment_121453752

    It doesn't matter what other problem you have that battery being drained to 7.6V yet again will seriously degrade the battery therefore you need a new battery even if you find and fix another issue.

    Wake me up when it's all over.



  • #41
    mikewest
    Registered Users, Registered Users 2 Posts: 761 ✭✭✭mikewest


    Have you brought the car to wherever you bought the battery and told them the battery is not holding charge. If you got a new one this year then that battery is under warranty. Get it replaced, may need to get firm with them. If the new battery is still giving trouble then it's either the alternator or a phantom drain.



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  • #42
    Igotadose
    Registered Users, Registered Users 2 Posts: 13,708 ✭✭✭✭Igotadose


    https://www.boards.ie/discussion/comment/121453776#Comment_121453776

    That's likely to be the next step.


    I remember in the old days you could test batteries with a gizmo that had little colored balls in it, I think you went from cell to cell and looked at how many floated. I expect those days are over, is there any other way to test a battery?

    BTW, we didn't care about safety as much back then (I'm thinking mid 1970's).



  • #43
    mickdw
    Registered Users, Registered Users 2 Posts: 23,406 ✭✭✭✭mickdw


    https://www.boards.ie/discussion/comment/121453776#Comment_121453776

    And would you go back and apologise and pay for the replacement battery if you then found it wasn't the battery.



  • #44
    mikewest
    Registered Users, Registered Users 2 Posts: 761 ✭✭✭mikewest


    Yes but most likely they would test the battery and find out if that one was faulty first, easy way to get a simple diagnosis of one possible fault.



  • #45
    mikewest
    Registered Users, Registered Users 2 Posts: 761 ✭✭✭mikewest


    If they sell a decent quantity of batteries they will have some form of tester or know there is a certain failure rate of the battery they supplied you with.



  • #46
    mickdw
    Registered Users, Registered Users 2 Posts: 23,406 ✭✭✭✭mickdw


    https://www.boards.ie/discussion/comment/121453863#Comment_121453863

    Ya but that's a different story to - go back, get firm and get it replaced.

    If it does happen to be battery in this case, testing will likely tell us nothing as its operating fine for periods then no start.

    I've seen battery cracked around the terminal behaving in this way and causing awful hassle.



  • #47
    Andrewf20
    Registered Users, Registered Users 2 Posts: 3,194 ✭✭✭Andrewf20


    Had a similar issue on my E36 recently. When the engine got turned off you could see the battery voltage drop approx 1 volt every 5 mins. I disconnected the positive battery cable and found 3 ohms resistance between it and the chassis. I pulled each fuse one at a time and rechecked the cable to chassis voltage each time until I found the fuse that when pulled out, gave open circuit. The fuse was for the interior lights and cigarette socket. It was a faulty USB charger plugged into the cigarette socket that was draining the battery but strangely not blowing a fuse.



  • #48
    mk7r
    Registered Users, Registered Users 2 Posts: 777 ✭✭✭mk7r


    https://www.boards.ie/discussion/comment/121454202#Comment_121454202

    It wouldn't blow a fuse unless the current draw exceeded the value of the fuse (20A). It could happily sit there and draw 15A all night long being faulty without anything happening except the battery going flat



  • #49
    pooley124
    Registered Users, Registered Users 2 Posts: 45 ✭pooley124


    https://www.boards.ie/discussion/comment/121453800#Comment_121453800

    The only way to properly test a battery is with a load tester.

    Your problem really sounds like something is draining it rather than a bad battery though. You should get a multimeter and test the current draw yourself. It's easy enough to do.

    Post edited by pooley124 on


  • #50
    Igotadose
    Registered Users, Registered Users 2 Posts: 13,708 ✭✭✭✭Igotadose


    5.6v on it this a.m.. Tried "Noco B20 boost" - first didn't detect it, then I tried the emergency override 3 times, nothing.

    Trickle charger on it now for about an hour, up to 7.6V. In another hour I'll try the Noco booster again and see if it'll turn over so I can go out and get a new battery for it.

    Frustrated: Draper multimeter said '3.6v" where the trickle-charger reads 5.6v. No idea why they're different, though the draper's hooked up with the battery attached to the cables, and the trickle the cables are removed. Does that provide any hints?



  • #51
    pooley124
    Registered Users, Registered Users 2 Posts: 45 ✭pooley124


    Don't think the voltage difference means anything. As I said, when the battery is charged put the car in the same state as it would be overnight, i.e everything off and doors locked, then test for current flow between the negative cable and the battery terminal.



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  • #52
    Andrewf20
    Registered Users, Registered Users 2 Posts: 3,194 ✭✭✭Andrewf20


    https://www.boards.ie/discussion/comment/121454325#Comment_121454325

    Exactly. I was just surprised it didn't blow something considering how fast the battery was draining.



  • #53
    tabby aspreme
    Registered Users, Registered Users 2 Posts: 4,009 ✭✭✭tabby aspreme


    Disconnect the battery overnight, to find out if the battery is faulty and discharging itself .



  • #54
    mk7r
    Registered Users, Registered Users 2 Posts: 777 ✭✭✭mk7r


    https://www.boards.ie/discussion/comment/121459737#Comment_121459737

    The problem is that won't really tell you anything as there is always some load on the battery when the car is off, disconnecting it completely is not a fair test



  • #55
    tabby aspreme
    Registered Users, Registered Users 2 Posts: 4,009 ✭✭✭tabby aspreme


    https://www.boards.ie/discussion/comment/121459892#Comment_121459892

    If the battery is good there should be zero or a negligible drop in voltage, if it drops a noticeable amount overnight while disconnected there's a problem with it



  • #56
    mk7r
    Registered Users, Registered Users 2 Posts: 777 ✭✭✭mk7r


    https://www.boards.ie/discussion/comment/121459996#Comment_121459996

    Absolutely thats true but the battery may not drop when disconnected but still be bad so the battery may "pass" the test but because there was no load its a false pass



  • #57
    Igotadose
    Registered Users, Registered Users 2 Posts: 13,708 ✭✭✭✭Igotadose


    https://www.boards.ie/discussion/comment/121459892#Comment_121459892

    What is putting load on the battery when the car is turned off?



  • #58
    mk7r
    Registered Users, Registered Users 2 Posts: 777 ✭✭✭mk7r


    https://www.boards.ie/discussion/comment/121460392#Comment_121460392

    There will always be a small but constant draw, modules such as the body control module need to stay awake to listen for central locking requests etc



  • #59
    Igotadose
    Registered Users, Registered Users 2 Posts: 13,708 ✭✭✭✭Igotadose


    https://www.boards.ie/discussion/comment/121462406#Comment_121462406

    Might be on to something here. Our key fobs stop working usually a couple of days before the battery drains. Could the body control module be the culprit? Maybe it's draining power somehow?

    We can always unlock the doors with the key even when the battery's drained, but the key doesn't unlock the boot (car is a hatchback.) I wonder if its the locking mechanism causing the problem. Thanks for this information (and thank everyone that's replied!)



  • #60
    mk7r
    Registered Users, Registered Users 2 Posts: 777 ✭✭✭mk7r


    https://www.boards.ie/discussion/comment/121462628#Comment_121462628

    It's unlikely to be the body control module, it's supposed to draw power as are other modules, the battery just needs to be healthy enough to cope with that draw over and extended period.

    I'm still leaning towards your battery



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  • #61
    Igotadose
    Registered Users, Registered Users 2 Posts: 13,708 ✭✭✭✭Igotadose


    https://www.boards.ie/discussion/comment/121462662#Comment_121462662

    But... can it (and other modules) be 'overdrawing?' If its out of spec somehow, could it be draining the battery?

    It's weird that the fobs stop working; sometimes, they start working again, best I can determine is that if I take the car on a fairly long drive it charges the battery enough that the fobs work - but that's not precise enough, since the car runs fine without the fobs working. And, sometimes they start working again.



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