Alternator going bad?

[01BlueTahoeGuy]

Ok, about 6 months ago, I replace the battery in my 2015 Yukon SLT.

I changed it because I was having issues with the infotainment system, plus it was the original one.

We have been having issues again, so I am looking at it today.

I checked the battery voltage and it was 12.3v.

So I hooked my 4 amp battery charger to see what would happen.

It jumped to 13.6 and the indicator showed the battery was half charged.

I am fairly decent at understanding electrical, so on leaning towards the alternator not charging properly, I don’t have a tester.

My wife drives it daily, and it hasn’t failed to start since I replaced the battery.

Anyone else run into this?

 

[blondie70]

All looks ok to me...but the meter at half charge..maybe wacky meter ?

 

[Fless]

If you powered up (110v) your charger when the voltage went up, that's the charging voltage. But if your charger reads voltage without AC, then I don't know what to say.

Short trips don't allow for the charging system to completely fill the battery, so if your wife's trips aren't long enough to get things charged up after starting, you might want to consider taking longer drives.

 

[OR VietVet]

When checking the battery voltage that showed you 12.3 volts, start the engine with that meter hooked up and see if the voltage shown jumps up. That would indicate the alternator is charging but will not show the amps. You can watch the voltage and as the vehicle idles, turn on blower motor and headlights and whatever else you can turn on, like wipers. Watch for voltage to drop but then climb back up to what it showed at idle. That would indicate the voltage regulator is reacting to a load and catching up on the charging.

Should do a complete charge and then load test battery and see if it holds above 9.6 volts for 15 seconds.

 

[01BlueTahoeGuy]

Well, left the charger on it until is showed green.

Fired it up the with my multimeter hooked up, and it was at 14.3v.

Turned on the blower and such, no drop.

The drives are 45 to an hour each way.

But the infotainment system was working fine after I did all this ( which is why I was checking everything) after the battery was fully charged.

The rig had only sat for 12 to 14 hours….. so curious as to why the meter on my charger was reading low, it only took 20 to 30 minutes to top it off.

So now I am not sure what the issue is.

I know these things are super sensitive to battery voltages being low.

 

[swathdiver]

Keep an eye on it.

Without a Tech-2, a good way to check the battery's state of charge is to put the meter to it in the morning after it has sat all night. Check the voltage and ambient temperature against a chart and that will give you a close approximate state of charge. GM considers a battery wore out if the state of charge is below 65%.



The battery might need to have its plates de-sulfated so see if your tender/charger handles that. I got another year out of a battery with my tender and that battery had been run to the single digits dead a couple of times.

 

[01BlueTahoeGuy]

Will check.

This battery is an Interstate not even a year old…..

 

[the 18th letter]

I’ve read the battery cables on these can look fine but have corrosion inside, somewhere on the site there’s a post on how to test them. Corroded grounds have also been know to muck up the electrical system in these.

 

[01BlueTahoeGuy]

Ok, while out driving today, the voltage gage on the dash dropped to just above 9v a couple of times then went back to 14v.

I pulled the alternator out and took it to AutoZone and it tested as good.

I am wondering if there is an intermittent issue in the alternator, I have checked the cables, can’t find any corrosion and all the connections were tight.

I am leaning towards getting a new alternator, but am having sticker shock as the parts stores want 380 and up, Rockauto is 250.

Any thoughts or others troubleshooting anyone can recommend?

 

[OR VietVet]

You saw it intermittently working on the gauge. Attach a DVOM with long enough leads, and drive it again.