Alternator / Battery question.

[generik777]

So I was on the way back from a trip yesterday. I turned the key and the car just clicked. So I had a friend give me a jump start, and the car started right up. So we pulled out on started to make our way home. During the drive the voltmeter in the dash read just barely under 14. After driving for about 3 hrs we stopped at a rest stop. When I went to start the car again. Same thing happened, It just clicked. Got another jump start and drove the next couple of hours home. Got home parked the car in the driveway and it wont start again unless I jump it. My question is, Would this be a bad battery or a bad alternator? I want to say it is the alternator but then why does the voltmeter read around 14 when driving? Or maybe it's a combination of both. Any help appreciated.

[MattzWarsteiner]

Could be a bad connection on the battery. Check them first. If the cables and connections are good, its the battery. Get it checked for free at like Autozone or Advance.

If you show near 14V on the gauge, then your alternator is working fine.

[generik777]

Ok, I'll Probably do that first then. I hope that's it since it's the cheaper of the two.

[Seerlah]

Your battery starts your car and then your alternator does the work after that. The battery only holds ~12.5 volts of charge while the alternator produces ~14.2. You were driving on your alternator, which is a good thing (and how your vehicle is supposed to operate). The battery is just there for start up (then alternator does the work), luminares such as dome lights, map lights, cluster gauges, radio, etc(all while car tuened off).

Your alternator is still fine. It seems like your battery is shot. You could be posotive by placing a volt meter to it and getting a reading of the charge. But from what you wrote, I can tell you your battery is dead.

-to check alternator you need to start the car (jump start) then unhook the posotive feed. If your car still runs, then it is your battery (should be ~12.5v)

-to check battery, you need to get a volt meter and check the charge. or you could turn your key to the last click before ignition and look at the cluster battery meter (should be ~12.5v)

[MattzWarsteiner]

^^ ^ ^^ Agree with almost everything but... NoOoOO don't disconnect your battery with the engine running.

If you want a DIY test for the alternator:

Note the volts before starting.

Start the car, should be +1 to +2 within a few seconds. Looks good so far?

Now add loads, use the AC with fan on hi, lights on, seat heaters and rear defrost = whole lotta amps.

You may have to advance the idle to 1000 or so, but the voltage should remain at least above 12V and eventually rise.

Its a rough check but won't p!ss off any modules or other stuff.

[generik777]

Well, i went up and bought a battery. They said it was for my car and that it said something about being vented to the outside, I already knew this because of the hose going to the front of the current battery. But I got the new one home and am looking at it and don't see anywhere to hook the venting hose to. Is it ok to just not plug it in?

[generik777]

well, I got the new battery installed and car starts and runs good now. But I think I may need a new alternator as well. Cause the voltmeter reads 14 until I turn the AC and lights on, Then it goes down to about 13 or maybe even a little less. That means time for an alternator, Right?

[MattzWarsteiner]

Is this 13V at idle or driving around ?

When you are driving at speed the voltage may not get all the way to around 14 but will probably go above 13 soon eventually with a load. The target voltage is 13.8, best read with a meter.

The alternator is rated for max output at speeds above 1000 rpm. Idle speed only allows a limited amount of current from the alternator. The rotor inside needs to turn faster to move more electrons for the higher loads.

A hose huh? Man i dunno about that one. I have a 98 V6 but will have to look for a hose, but then I don't have the original equipment type VAG battery now either.

[generik777]

It's about 13 at idle. I'd say it's at about 13.5 when driving around town. Although sometimes at stop lights it may dip a little lower than 13 when I have the AC and such on.

[MattzWarsteiner]

Alternator is good.

[AudiRacerS4]

It's about 13 at idle. I'd say it's at about 13.5 when driving around town. Although sometimes at stop lights it may dip a little lower than 13 when I have the AC and such on.

thats normal

[njm23]

I would check the grounds as well. That exact thing happened to me, and they even tried telling me my alternator was bad since they base it off the battery at advance auto. It was the ground to the starter.. Something triggered your battery to die, unless it was just really old. So your problem may not be gone..

[generik777]

Sweet, Thanx. That's what I was hoping for. Any more input on the venting hose situation. I did a little searching around on AZ and saw a few other people that just left it unplugged cause there was nowhere to plug it in, So I guess I'm not that worried.