Battery light came on and voltmeter reads slightly below 12V: what is going on?

[jlee]

You shouldn't be seeing 18v off a car battery- doublecheck your multimeter.

Originally posted by: mshan
Anyone think it might be prudent to buy a car battery charger like this ( http://www.amazon.com/exec/obi...ATVPDKIKX0DER&v=glance ), and fully charging battery before attempting to drive to dealer (less than 10 miles away)?

Also, does an alternator fail all or nothing, or just gradually?

Initially, when I noticed light I had ac on; I turned it off and the voltmeter moved slightly higher (though still right under 12 V).

And does progressively sagging voltage means battery is getting more and more drained?

In this case, I would go with 'yes'.

 

[LTC8K6]

If it were my car, I would indeed charge the battery up before attempting to drive any more.

 

[mshan]

What do you guys think of this car battery charger: http://www.amazon.com/exec/obi...ATVPDKIKX0DER&v=glance

It showed up at top of Amazon search for "car battery charger" (I don't see plug, but I assume this is plugged into electrical outlet to work?)

 

[LTC8K6]

It's a good charger when you aren't in a hurry.
Those are also available at any Wal-Mart.

 

[Suspicious-Teach8788]

Originally posted by: SJP0tato

Originally posted by: mshan
Can I take it to somewhere like Autozone and get battery and alternator tested?

Or do I have to got dealer?

Also, can I damage car by driving it, or can it suddenly just stop at any point?

What else could it be other than alternator?

I guess it also makes sense to just take it to dealer (there is one garage that maintains BMWs, but I don't know how willing they are to work on Audis).

Autozone and other parts stores have the equipment to run basic tests on the battery and alternator. Usually this is all that's needed 99% of the time, and it's free.

If the problem is the alternator, you're running on whatever charge is stored in the battery. Eventually you'll use up enough that the next time you go to start it there won't be enough power to turn the starter and you'll be stuck until you use jumper cables to "jump" the battery. Less likely is the car could stall out during driving because of lack of power.

Other than the alternator or battery it could be corrosion on the battery cables, loose connection to the battery itself, a loose ground wire, corroded wires leading to/from the alternator/battery.

Not very common in theory, but I've seen it happen twice (not to me). I had to rescue several friends because of this.

Definite head out to Autozone and get it tested if it's free. I've never had an alternator go bad, but the thought is scary. It's like a fuel tank with a hole in it. You can always gas up (jump) your car, but your car can die in the middle. I've only had to deal with bad batteries that need frequent jumps if not used in 2 weeks which IMO is better. At least it charges and your car won't die in the middle of the road.

 

[mshan]

Called the independent Audi garage that I take to car when I visit my parents in NY and they said it could just be an old battery (last replaced 2001, 2002, or 2003). e. g. saying alternator is charging but some cells of battery have failed.

He said his wholesale price for Bosch 90 amp alternator were around $300 - $350, 120 amp around $300 (both rebuilt), and said only other alternative I should consider is Valeo.

Also said shouldn't have to take bumper off car and his estimate of labor was just 2 hours. Unfortunately, they are over 500 miles away and don't think car would make it there.

Also recommended looking for garages that service Volkswagen.

 

[LTC8K6]

With some cells out in the battery, your dash volmeter would still show a good alternator with the engine running. According to your OP, the voltage was low when the engine was running.

Also, a battery with some cells out is probably not going to start your car.

I would replace the battery anyway, as it's quite old, but I'd be suspicious of that alternator.

 

[LTC8K6]

I'd just go and let Auto Zone test the battery and charging system. They will have a load tester which will put a load on the battery.

 

[bruceb]

Alternator failure can take the form of a bad diode. If a diode opens, the volts will go down. If it shorts the output volts will go up. An alternator can also fail due to a bad internal voltage regulator, in which case it will not output the proper voltage based on RPM and current draw. An alternator can also fail to do any charging due to worn out brushes not making contact with the rotor.

 

[LTC8K6]

Yeah, I already mentioned a bad diode...

Time warpage...

 

[LordMorpheus]

Originally posted by: hanoverphist
sounds more like charging system than battery to me

yep. You should see in the neighborhood of 14 volts in the car when it's running. If it's lower than that that means your alt is toasted. More likely, it's just a diode or something, but usually that's all packaged in the alternator and replacing the whole unit is the only realistic option.

 

[mshan]

Took it to an independent Audi garage and they said both alternator and battery were bad.

Rebuilt Bosch is going to be either $400 / $475 (90 amp or 120 amp, depending upon what is already in car), with 3.5 hours labor @ $80/hr (Interstate battery is $150 installed).

Independent Audi garage up in New York where my parents live was $300 / $350 + 2 hours labor @ 75/hr, but don't think it would be safe to drive 500 miles to get there.

 

[bruceb]

Might as well spring for the bigger capacity alternator. It will work easier and give you more power for accessories and in general is better overall.