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Discussion Starter · #1 ·
My battery light went on today and I can't say for sure what the issue it.
I did read the Battery tutorial posted by Stickey. Nice resource.

I drove home, about 15 miles on the highway with all accessories off. The light never went out.

When I got home I did the following measurements:

Battery open voltage with the engine off is 12.7v. That indicates a full charge at 40 degrees F.

The voltage across the battery terminals while running at idle is 14.4 volts.

I know in the past it I have measured 14.5v or even 14.6v. Still 14.4v is still a good charge being put out by the alt.

When I put the lights at idle it stays at 14.4v.

The connections on top seem good. The battery is one year old. The water in the cells are covering the plates.

Any ideas?
 

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Good trouble shooting checks.

Check the serp belt back side physical condition & it's tension, by looking at the tension range marks on the tensioner arm, to make sure it's indicating that belt tightness is within range.

If the back side of the belt is missing chunks of rubber, or it's tension isn't in spec, the belt could be slipping on the alternator when it's under load, or the engine is reving, or if the belt s wet.
Make sure there isn't any oil or coolant dripping on the belt or a pully.

If all thats ok, check the electrical connections at the battery & alternator, they should be clean, bright & tight.

If thats ok, check the battery to engine & body ground points, they too must be clean bright & tight.

If all thats ok, maybe consider running this puppy by your favorite autoparts store, for a no cost, in vehicle, electrical system check up, via their portable electrical system tester.

Expertly used, it can properly load test the alternator for a slipping belt, weak or shorted diodes, the battery for weak, leaky, or shorted cells, the battery cables & their connections for under load voltage drop & will likely be able to pinpoint the problem.

Some thoughts for consideration, let us know what you find.
 

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Voltage at idle shouldnt be that high. What is it at 1500 RPM?
 

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Discussion Starter · #4 ·
Ok....What should the voltage be at idle?

I need to get a helper to check it at 1500 rpm.

For some reason the light went out. Strangly, it has been even colder with temps around 20F.
Go figure.
Thanks
 

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Discussion Starter · #5 ·
Now the light is back on again.

The battery voltage at idle was 14.6 and when I put on all of the accessories including the high beams it drop to about 14.5.

Have not had time to check all of the grounds/connections but those near the top with easy access seem ok.

It is too damn cold to have to deal with this right now.
 
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