99 audi a6 with 189k miles on it..its been sitting on the garage for awhile now. Tried to turn it on no lights on the dash came on. It won't budge at all...I jumped it, it eventually turned on let it run for about 5 to 10 minutes. I turned it off put it back in the garage. Then I tried turning it back on a week later, the same thing. Right now I'm charging the battery up with a charger. Any ideas? bad battery? bad cells? or dead alternator?

 

I say charge the battery and see what happens. 5 or 10 minutes of charge with alternator will not charge the battery enough to crank the car.

 

Okay, well it's charging now, once the car is on should I leave the charging cables on it. Turn it back off, then let it continue to charge?

 

You won't really be able to differentiate between battery with dead cell(s) or a failing alternator. Get it started and take it to an Autozone (or equivalent) for a free battery and alternator test. Just don't turn it off when you go in to talk to them.

If it's not driveable, I suggest leaving it on the charger for 24 hours at lowest power. In theory, that should charge the battery fully. Disconnect the charger and try to start it a few times. If it fails to start after a few tries, you probably have a bad battery.

It's tougher to determine if the alternator is good because you are not really running the car enough for it to fully charge the battery. See the Autozone suggestion.

A better electrician than me may suggest some tests with a voltimeter.

 

I'm an electrical engineer and someone who has worked on cars most of my life, so here is my two cents...

In almost all of these cases the battery is culprit. The alternator is not much more than a magnet, some wires and a few diodes. So there is not much to fail. That having been said, they do occassionally go bad. The battery is only used to start the car. Once the engine is running, the alternator supplies the electrical current to the system. On older cars (pre engine computer) a simple test to determine a bad battery versus an alternator was to get the car started and remove one of the battery cables while the engine was running. If it continued to run, the battery was bad. If it quit immediately, the alternator was bad. I would NOT recommend this test on newer models since there is a risk of voltage spikes damaging the car computer when the battery cable is removed while the engine is running.

Some things to try - make sure the battery cables are free of corrosion. If they are corroded, this can limit the amount of current to the system. To clean them, disconnect them from the battery and dissolve the corrosion with a mix of water and baking soda. Once clean, dry the cables and battery posts and use some sandpaper or wire brush to ensure a good contact surface on the terminals.

If you have a friend with a voltmeter or multimeter, you can check the alternator output. Measure the voltage at the battery while the engine is running. If the alternator is good, it will put out about 13.5 volts - maybe slightly more. Anything less than that is an indication the alternator (or charging circuit) is bad.

Lead-acid batteries have a finite life. If your battery is more than 3 or 4 years old, its time for a new one. You may get some more service out of this battery but with age the cold cranking amps (CCA) will diminish and battery will disappoint you in cold weather or sometime when you least expect it.

If you don't have the tools or time to try these, I would take the advise of the other posts and go to Autozone for the tests.

Hope this helps, Jim

 

There's a way I have used for checking if the alternator is bad and it needs no special tools. Get the car started, let it idle, turn on the heater fan and head lights so there is a good draw on the electrical system. Now if you are on your own shine the lights at a wall and lightly rev the car. You should be able to see the lights brighten a little and hear the fan speed up a touch. If this is the case then the alternator is fine. This test has worked for me on both motorcycles and cars.

 

Thank you everyone for your input!

I've had a battery charger on the car now for about 22 hours now. Still no lights or any electrical on the dash work, I have to settings on my battery so I'm going to switch it out and use more voltage, than what I am currently and see what happens.

 

A question... the 2 setting on your charger you are referring to... You did not set it on 6V did you? It won't charge with 6V. Make sure it is on 12V and on the higher AMP setting.

 

Only use the high amp setting for a short time,a few hours at most or if your battery is ok, then you'll boil it up and kill it. Low amps, the lower the better, for longer periods is better. Someone maintenance chargers can even receive dead batteries by using super low amps over a few days.

 

The alternator on my 1999 A6 failed at something over 200K miles because the area on the shaft where the brushes (or whatever the pieces are called that make contact with the shaft) made contact had worn down so badly that one of them was no longer making a good connection.

FYI. For your sake, I hope it's the battery. It's cheaper and about a thousand times easier to change. Good luck.