Alternator voltage question 2010 GMC Sierra 5.3

Mrjoshua74 · March 8, 2021

Ever since I upgraded to an AGM battery about 5 years ago, I’ve noticed that my voltage meter stays around 14 volts. No fluctuations at all. My alternator is an AC Delco DR44 160amp. Right after start up, using a voltage meter, the volts on the alternator are between 13.72 and 13.90. The tests about the same. I turn on my high beams, the heater full blast, engage tow haul mode, but it stays exactly the same. Would love to hear your thoughts. Thanks!

CamGTP · March 9, 2021

Sounds fine to me. With a regular battery I saw it go down to 13.5 and up to 14.8 depending on the needs of the charging system.

swathdiver · March 9, 2021

10 hours ago, Mrjoshua74 said:

Ever since I upgraded to an AGM battery about 5 years ago, I’ve noticed that my voltage meter stays around 14 volts. No fluctuations at all. My alternator is an AC Delco DR44 160amp. Right after start up, using a voltage meter, the volts on the alternator are between 13.72 and 13.90. The tests about the same. I turn on my high beams, the heater full blast, engage tow haul mode, but it stays exactly the same. Would love to hear your thoughts. Thanks!

I would think that if the alternator has to run at full output all the time, it might be time for a new battery. I read somewhere that the charging system for the GMT900s was not designed for AGM batteries, something about charge rates. I cannot remember where I read this and while ACDelco makes AGM batteries, they do not recommend them for the 900s.

My alternator frequently drops down to 12-13 volts as the battery is fully charged while cruising.

garagerog · March 9, 2021

I believe swathdiver is correct. PCM controls alternator charging rate, so programming was probably changed to deal with the start/stop function and GM does call for AGM batteries in all vehicles with this function.

MaverickZ71 · March 11, 2021

On 3/8/2021 at 2:03 PM, Mrjoshua74 said:

Ever since I upgraded to an AGM battery about 5 years ago, I’ve noticed that my voltage meter stays around 14 volts. No fluctuations at all. My alternator is an AC Delco DR44 160amp. Right after start up, using a voltage meter, the volts on the alternator are between 13.72 and 13.90. The tests about the same. I turn on my high beams, the heater full blast, engage tow haul mode, but it stays exactly the same. Would love to hear your thoughts. Thanks!

Interesting. Our '09 Silverado (5.3L Z71 4x4 crew cab LT) is essentially doing the same thing now. When new, the needle on the voltmeter would constantly swing back and forth anywhere between 12 and 15+ volts on the gage, depending on charge, load, outside temp, etc. Now it just stays on 14 volts when it's running. And ours is on its 3rd battery, with the last 2 being Everstart Maxx H6's from WalMart, which are not AGM batteries. Wonder if it's because our alternators are getting up in years?

Edited March 11, 2021 by MaverickZ71

Sharpz · March 11, 2021

3 hours ago, MaverickZ71 said:

Interesting. Our '09 Silverado (5.3L Z71 4x4 crew cab LT) is essentially doing the same thing now. When new, the needle on the voltmeter would constantly swing back and forth anywhere between 12 and 15+ volts on the gage, depending on charge, load, outside temp, etc. Now it just stays on 14 volts when it's running. And ours is on its 3rd battery, with the last 2 being Everstart Maxx H6's from WalMart, which are not AGM batteries. Wonder if it's because our alternators are getting up in years?

Both your trucks are getting age on them, so I wouldnt put 100 percent confidence in those gauges. A voltage meter will tell you the true story.

Mrjoshua74 · March 17, 2021

*UPDATE* I now have a new battery, a Duralast Gold. So far, after driving a good bit yesterday, it’s still hovering around the 14v mark, maybe just the age of the truck. And my alternator is not that old, maybe 5-6 years tops. I do however need to change my serpentine belt and install a new belt tensioner. I’m going to ask the GMC tech next week about it, when I take it in to have finally have the airbag recall fixed.

swathdiver · March 22, 2021

What makes sense is that your batteries were needing the full output of the alternator to get fully charged. The computers in these trucks monitor the health of the battery and one can see this data via a bi-directional scan tool like the tech-2.

Old_Chevy_Guy · April 10, 2021

This thread caught my eye. I have a 2007 Suburban 1500 5.3L V8 with just over 200,000 miles. I have used NAPA Gold batteries for years, and my Suburban consistently registered 14V while driving since I bought it new in 2007. Last year, I replaced the alternator since it was original to the vehicle and around 180,000 miles of use. I noticed immediately that the voltage gauge would oscillate between ~12 to 15V during driving, but I never had issues with the vehicle systems (lights, radio, seats, etc.). My experience was that the older alternator was pegged at 14V output whether I was using an old or new battery (sealed lead acid usually although one may have been serviceable). The new alternator, which I believe was the heavier duty version (>150 amps maybe?), is able to adjust the system voltage depending on the battery's charging needs. You may have moved on from this thread already, but I thought I'd toss this out there in case the problem is still gnawing at your mind from time to time. Good luck.