Hello:

I may have an issue here, I would welcome feedback, please. This is for a 2004 coupe, with 137,000 miles, in good condition.

The history:
I was out one evening recently, and stopped at an intersection for a longer than usual time due to a traffic issue ahead of me. By coincidence, , I had the battery voltage up on the DIC. During this prolonger standing stop (in drive with foot brake applied) the battery voltage reading began to drop starting from 13.8 and each step until it reached 13.0. Now once driving again, it resumed its normal 13.8 to 14 reading. While stopped there was nothing running expect the engine and the headlights.
The next morning, after the Vette had rested for 12 hours in my garage, I tested the battery. It was 12.3. I noticed the age of the Optima Red Top was slightly over 3 years old. That is old for a battery in the metro Atlanta area. I replaced the battery with a new Optima Red Top, I performed a cold test with a meter, and it was 12.6. Turned the Vette on, while running it was 14.1. I kept it running then turned everything on; radio, AC, wipers. Tested it again, and 14.1.
Afterward, I get again in prolonged stop and it begins to fall again.

The question:

Is this a problem? Would it be the alternator? Serpentine belt? I ask as I must leave in a few days to visit very rural southern Georgia. I would really, really would not want to have an issue while there. I did a recent short drive for a couple of hours on the interstate and there and back the meter was 14.1 or so at all times.

Thank you

 

First question is where are you reading these voltages…on the DIC or with a DVOM across the battery terminals ??…as you can see in the picture the DIC voltage is around .4 volts lower than at the battery itself…so with a load…AC, blower, headlights on what does it drop to…14.1 ??…what voltage at the battery if lower than that ??…14.1 is fine…it is a always a good idea to to a voltage drop test on the positive and negative side of the charging system…with DVOM place the meter leads from battery positive to the B+ of the alternator and on the negative side from battery negative to the alternator case….this is done with the charging system under load and at around 2500 RPM or so….you should see around .1 to .2 volts as you can see in the other 2 pictures on my car…GM’s values are .5 volts.


Negative side voltage drop

Positive side voltage drop

 

Hello. I thank you for taking the time for such a well thought out response. To respond to your question to me, I used a meter on the battery terminals only. As mentioned, on that test, the numbers were fine. It was only on the DIC, at a standing stop only, was the numbers on the DIC slowly dropping. My only action was to replace the battery, I did that as it was showing as slightly over 3 years old. My thought was, in my local environment, 3 years on a battery is a long time. Before I did the replacement, my old battery, on doing a cold test, after the Vette had sat overnight had 3 successive drops in the reading with the aforementioned reader. The readings were 12.6, 12.3, and then 12.03.

 

Have you checked for parasitic loss when the car sits overnight? You might have something pulling it down.

 

Batteries life is less in you live in warm climates like
Georgia and worse yet for me here in Southwest Florida…as you can see below the voltmeter comes from the IPC module from fuse 19 through the fusebox and if you follow that upstream it goes through the ignition switch so you can see why there is a .4 volt drop in voltage…it can also be some oxidation starting to show up on the ignition which our Corvettes and other GM platforms have issues with…I would still do that charging system voltage drop check to make sure the wiring is up to snuff

 

Thank you for this suggestion. I did the test and the initial result was .082. I did not leave it out for long. I will test again tomorrow and leave it on for a longer period of time. Perhaps there is something that goes to sleep after the other things shut down. The result did not shock me, but it seemed a tad higher than I would have expected.

 

I remember .082 when measuring sleep mode current on my car, I had to wait about 20 minutes for the car to fully enter sleep mode. You should have .025ma when the car is in sleep mode, just wait a while longer.

 

I did the test again, and waited 20 minutes.. The reading was .013. As you, I had wondered id a longer wait time would provide a different result.

Thank you for your suggestion.

 

Your Welcome, I measured sleep mode current convinced that something was drawing my battery down, but it was just my battery needing to be replaced.