2007 Corolla; Battery light fading away?

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Hey all, recently noticed after starting my car that once started and I turn my lights on, I notice the battery light lights up somewhat and then fades away..just the battery light, the dash lights and all else do not dim and no driveability issues..no trouble starting and after it does it from a cold start (even if car was plugged to blockheater for 4hrs it still occurs. After it happens on first start of day I no longer see it occur unless parked for some time. Previous vehicles I know itd be the alternator because the lights would dim when accel or braking and it would just go...my battery was replaced about 8 months ago but alternator is original so I am thinking alternator most likely..i also hear a bit of sound like from a belt, not exactly a whining sound more like a dragging sound hard to explain. The belt is a gatorback that seems firm and appears to move normally when running. I realize I should just test batt and alt with a multimeter but I dont have a garage and its cold out. I certainly will test it in the next couple days but am curious if it could be something minor besides the alt? Is it just an early warning sign that its going out? Obviously this occured now when money is tight, but just wondering if I have much time before I end up stranded...just looking for other possibilities or easy things I can check, if not thats fine, like I said, I know I need to test the alt and battery first with a multimeter. Thanks in advance!
 
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Test the battery with a Midtronics tester or carbon pile load tester. A multimeter is not a great test meter. If original then test the alternator and replace the battery.
 

Rolla07

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Originally Posted By: Donald
Test the battery with a Midtronics tester or carbon pile load tester. A multimeter is not a great test meter. If original then test the alternator and replace the battery.
Thanks for the advice! Those testers are pricey! The alternator is the original, battery is new. (8 months old)
 
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Belt is slipping when amps are demanded. The fading away is the belt regaining traction on the pulley and driving the alternator more directly. It's a good sign for your battery that it's internal resistance is low enough to cause such demand for said current, but you may need to re-tension or clean the belt/pulley grooves from potential grease contamination. The gatorback has serrated serpentine channels IIRC so perhaps the lower surface area may not be ideal if tension and contamination check out.
 
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Since the battery light came on when the headlights were turned on I suspect it's the alternator. Have it tested because this may be your only warning to replace it ASAP before you get stranded in the cold.
 

Rolla07

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Originally Posted By: PeterPolyol
Belt is slipping when amps are demanded. The fading away is the belt regaining traction on the pulley and driving the alternator more directly. It's a good sign for your battery that it's internal resistance is low enough to cause such demand for said current, but you may need to re-tension or clean the belt/pulley grooves from potential grease contamination. The gatorback has serrated serpentine channels IIRC so perhaps the lower surface area may not be ideal if tension and contamination check out.
I wonder if spraying the belt with belt dressing is a good or bad idea...
 

Rolla07

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Originally Posted By: Donald
So if belt is slipping maybe a belt tensioner.
Yeah, was just thinking that..the belt seems quite firm to me so its odd but this could very well be it..
 

Rolla07

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I checked voltage on the battery and while car running and both normal. 12.78 and 14.26. Checked idler and pulley both were firm and appeared to be solid. Guess thats the extent of my diagnosis skills lol. The belt also appears to be fine.
 
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My original toyota alternator died around 12 years/160,000 miles Didnt realize the alternator was dying until it was completely gone. Slow weak start and then Id get going to about 20 mph and die, then the electric starter would kick in, die, And repeat. I could go about 35 mpH. Just driving like normal except the car died and turned on then died and turned on lol This sounds bad, but it worked long enough to get a couple miles to the shop. Dont be like me lol good luck
 
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