Battery light comes on while driving, goes out

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Was just starting a drive tonight and of course it's dark, noticed my dash lights were slightly dim and sure enough two seconds later the little red battery icon came on. I pulled over and checked the connection they seem OK. This is a side post battery in my Buick, an autocraft gold about 1.5 years old under warranty. I drove back home got my digital multimeter and after shutting the car off and sitting for a second the charge is 12.6 which is full if resting for 6 hours but not ideal for just shut down. Unfortunately I had to head to the ER which isn't far away so I pressed on. I tried keeping it in second gear to see if the increased rpm would help and it seemed to put the light out but not instantly. It seemed to go out faster when coasting down from 45 mph but when sitting idle at stop light it came back on. I put it in neutral and held at 2,500 rpm which may have helped but the light went off just not right away. It seems to go away when accelerating faster than 2,500 in neutral. Now It's late at night and hoping that it restarts after I get out of the ER, will have to figure out if it's the battery or alternator. I plan on fully charging the battery tonight if I make it back home and taking it to where I bought it to get everything tested. Kind of leaning towards alternator but not sure. If it is the alternator I need to decide where to purchase one. Had bad luck with Autozone lifetime warranty alternator on my Taurus, took 4 bad ones to get a good one. I have an alternator shop I am going to call in the morning or I am leaning towards Ultima new units from O'Reilly. My choices are Autozone, Advance, O'Reilly, Kentucky motors or Parts Plus. If it's the battery it has a 3 year warranty. Just had both tested less than 6 months ago working fine too with the aap tester on vehicle.
 
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My guess would be a weak voltage regulator which is normally part of the alternator these days. I would still get the battery tested though, they can go at any time and heat does kill batteries.
 

Nick1994

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My brother had a 99' Century and it would kill the Autozone Duralast batteries often. Same with my moms 03' Buick Rendezvous. Take it in to an auto parts store and they'll tell you if it's an alternator or battery
 

901Memphis

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The car in question is the buick century. There are so many choices for replacement alternators I don't know what to get. Rockauto has new Remy units but not sure of the quality. Rockauto has AC Delco remanufactured but very pricey. Advance Auto has Bosch new units and I can use the $40 off 100 but still pricy. Lucky I do have the Taurus so I can wait to repair the buick til I find my best option.
 
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Originally Posted By: 901Memphis
Now It's late at night and hoping that it restarts after I get out of the ER...
Am I the only one who noticed this? That's BITOG dedication. Or addiction.... shrug
 
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It's your alternator. I'd frankly try a junkyard. It's possible if not probable that you have a body control module or other computer controlling the alt, and your alt is still putting out "some" power, but the computer is sensing low voltage and complaining. The "idiot light" behavior is subtly different than it was in the 80's. If you have three diode bridges, two could be shot, for example.
 
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AAP will load test your battery for FREE! Take it there and get this done! AAP may[MAY] also have the means to test the alternator but, I don't know. Get this done as well, anywhere!
 
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I would use kentucy motors (koi). they, as well as parts plus (smyth), seem to supply most garages in the area.
 
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Originally Posted By: Wolf359
My guess would be a weak voltage regulator which is normally part of the alternator these days. I would still get the battery tested though, they can go at any time and heat does kill batteries.
There is no regulator on this unit. The PCM controls the voltage to the field, thus controlling charge.
 
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Not sure who your alternator shop is, but Maysville Generator has fixed a few for me. My MIL's old '90 LeSabre has the same problem, eats alternators, but fortunately on her 3800 it's right on top of the engine, easy change-out.
 
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Given that you already had the ability to measure the voltage, what stopped you from measuring the voltage when the car was running? I don't quite understand how you would skip that part.
 
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Check the positive terminal on the battery for corrosion - mine looked great on my Pontiac until I removed it. I had to pull the bolt from the assembly and wire brush everything. Saved me from buying a starter motor which I originally thought was the problem. The alternator started charging more as well after the repair.
 
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It's for sure the alt but a weak or damaged battery can kill an alternator to so get it tested as well. I always test both at the same time.
 
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Check your belts and tensioner. If the belt is slipping it could cause the problem you described.
 

Nick1994

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The alternator is easy to change on Centurys. Be careful where you get a battery tested, I have a 70' VW and I was questioning the battery and had it tested at AutoZone (it was an Oreilly battery) and Autozone tested and said it was bad. Took it to Oreillys, they tested it was fine.
 

901Memphis

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When I left after sitting for 4 hours the battery was at 12.4v and after starting it reads 14.40v. This appears to be right on the money for charging. Not sure of the mileage on the alternator since I had an engine swap but it's a Delphi so probably original to the car. Before I pulled the battery and charged it at 10 amps the charger indicated it was about 75% state of charge and 12.5v, so not sure what's what yet. I am going to have the battery tested now that it's fully charged and if it tests good I guess I'll replace the antique alternator.
 
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Intermittent problems suck. If it consistently varies with RPMs it is probably the alternator (brushes/slip rings). I'd avoid the auto parts store units if possible. Pull the alternator, take it to the alternator rebuild shop, they will likely be cheaper than new or reman parts house units. No need to pay for a new unit if all yours needs is a few parts.
 
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