Bad bettery vs. alternator?
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  1. #1
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    Bad bettery vs. alternator?

    My Jetta didn't start this morning, so I dropped it off at my repair shop. How can I tell that it is a bad battery vs. a bad alternator? No alternator warning light appears. The car is only 3 years old. What will the mechanics do to bebug it? Is it process of elmination (i.e. alternator has creates current)?

    Thanks.

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  3. #2
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    Re: Bad bettery vs. alternator? (Rascal)

    A couple of questions....How many miles does your car have? Is your car parked outside?

    My BMW 528i had a dead battery w/ 38k miles and it was only 3 years old. It died with no warning either. One day fine , next day dead.

  4. #3
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    Re: Bad bettery vs. alternator? (jwaters943)

    No, it's parked in a garage. It was very cold last week (10degF) overnight, but lately not quite that cold. The car does have 54000 miles. Last night, it was fine. This morning, I could only start it by jumping.

    Suggestions on battery replacement? I hate to spend the money, but something decent would be nice.

  5. #4
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    Re: Bad bettery vs. alternator? (Rascal)

    Yesterday my battery died. With no warning either. I had just finished my suspension, went to take it on a test drive and nothing. A quick run to Sears fixed. My car is only 2yrs old with 57K.

    Errin

  6. #5
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    Re: Bad bettery vs. alternator? (B5 SportsWagen)

    You can test the battery with a machine that runs through a testing procedure involving quick-charging it, then loading it to see if it held enough of the charge. Any auto parts store should have one of these.

    Another option is this: Test the voltage across your battery terminals. Then jump-start the car, then test the voltage across the terminals again. It should read 12.5V or higher (14V is common) when the car is running. If it doesn't, the alternator isn't putting out enough juice.

    If your battery died overnight, either it's bad or something on your car was drawing current all night.

    They'll determine what the problem is quickly and get you going in no time.

  7. #6
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    Re: Bad bettery vs. alternator? (Rascal)

    I think the alternator is tested to see if it's charging, but I'm not sure how it's done. If they say your alternator is bad, maybe ask them to send it out to be rebuilt or buy a rebuilt one. It is a lot cheaper then getting new and your paying extra for a new shell where the rebuilt ones have all new parts except the shell is reused. At least that's what I did with my Vette's chrome alternator. I had it rebuilt. It cost about half of what a new one cost to have it rebuilt instead.

  8. #7
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    Re: Bad bettery vs. alternator? (Rascal)

    This you can do in your own driveway for FREE!

    OK..here is what you'll need. Another car with a good battery, jumper cables, a Digital Volt Meter, and a trusty friend.

    First check the voltage on the battery at the treminals. Make sure you are touching the battery terminals and not the cable connectors. You should read something around 11.5VDC or above. Then with the meter leads still touching the terminals have trusty friend bump crank but not start the car. The reading will most likely drop to around 8 or 9 VDC while cranking. If the reading comes back up after your helper stops cranking, the battery is more than likely good. If it doesn't, then head for Sears for a new DieHard.

    If the reading did come back up the 'First Aid' method then would be to clean the battery terminals and try again. Even if they look clean, they could still be corroded enough to partialy insulate the battery but not look it. Reconnect the terminals and try again. If it starts...Happy Motoring!

    If it doesn't, then jump start the car. As they say on TV "READ AND FOLLOW ALL MANUFACTURER'S SAFETY INSTRUCTIONS" Look it up in the owners Destruction...er..I mean...Instruction Manaul. Remove the jumper cables and take a reading at the cable connectors. You should read somewhere around 14VDC with the engine running. If not you are having a charging circuit problem. If you do read something around 14 VDC then your battery is more than likely toast.

    When you take the car into a mechanic they will probably attach a nifty gadget to your battery called a load bank or load meter. This will tell them in about 60 seconds what you just took 15-30 minutes to learn in your driveway.

    Two words of advice here. First clean you battery terminals and cable connectors at least annualy. It takes about 5 minutes and is good insurance. Second, READ THOSE SAFETY INSTRUCTIONS! A partially discharged battery will try to regenerate itself. This has the nasty side effect of generating hydrogen gas. This is the same stuff, in liquid form, that the Space Shuttle uses for fuel for the main engines. Get the picture!

    And trlyka has some very good advice. If it is a bad alternator opt for a re-built. About the only thing you back 'used' in a rebuilt is the case, amature casting, and possibly the stator windings if tested good. Everything else is new and warrantied! For about half the price an OEM replacement.

    Good luck, but for my money I'd jump start the thing and head for Sears *L*

    [Modified by SirJohn, 9:15 PM 2/18/2003]

    <![CDATA[This you can do in your own driveway for FREE!

    OK..here is what you'll need. Another car with a good battery, jumper cables, a Digital Volt Meter, and a trusty friend.

    First check the voltage on the battery at the treminals. Make sure you are touching the battery terminals and not the cable connectors. You should read something around 11.5VDC or above. Then with the meter leads still touching the terminals have trusty friend bump crank but not start the car. The reading will most likely drop to around 8 or 9 VDC while cranking. If the reading comes back up after your helper stops cranking, the battery is more than likely good. If it doesn't, then head for Sears for a new DieHard.

    If the reading did come back up the 'First Aid' method then would be to clean the battery terminals and try again. Even if they look clean, they could still be corroded enough to partialy insulate the battery but not look it. Reconnect the terminals and try again. If it starts...Happy Motoring!

    If it doesn't, then jump start the car. As they say on TV "READ AND FOLLOW ALL MANUFACTURER'S SAFETY INSTRUCTIONS" Look it up in the owners Destruction...er..I mean...Instruction Manaul. Remove the jumper cables and take a reading at the cable connectors. You should read somewhere around 14VDC with the engine running. If not you are having a charging circuit problem. If you do read something around 14 VDC then your battery is more than likely toast.

    When you take the car into a mechanic they will probably attach a nifty gadget to your battery called a load bank or load meter. This will tell them in about 60 seconds what you just took 15-30 minutes to learn in your driveway.

    Two words of advice here. First clean you battery terminals and cable connectors at least annualy. It takes about 5 minutes and is good insurance. Second, READ THOSE SAFETY INSTRUCTIONS! A partially discharged battery will try to regenerate itself. This has the nasty side effect of generating hydrogen gas. This is the same stuff, in liquid form, that the Space Shuttle uses for fuel for the main engines. Get the picture!

    And trlyka has some very good advice. If it is a bad alternator opt for a re-built. About the only thing you back 'used' in a rebuilt is the case, amature casting, and possibly the stator windings if tested good. Everything else is new and warrantied! For about half the price an OEM replacement.

    Good luck, but for my money I'd jump start the thing and head for Sears *L*

    [Modified by SirJohn, 9:15 PM 2/18/2003]

    [Modified by SirJohn, 9:16 PM 2/18/2003]

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