Battery gauge low

[Silver]

A couple weeks ago the truck sat for a week and I presume the dash cam drained the one month old battery to 10.8 volts. I recharged it and all is well.

But lately this has been the battery guage.

What do you think? Alternator going out?

This is an 07 Chevrolet Trailblazer 4.2. 148k miles on original alternator.

 

[JHZR2]

What does an actual meter indicate the voltage to be?

 

[MasterSolenoid]

I have one of those Voltage Meters you plug into the cigarette lighter.
It helps to determine a bad Battery or Alternator.
Engine OFF (battery) .... 12V+
Engine ON (alternator) .... 14.4V

For me, I could see the Alternator cutting-out every 5 minutes.
A new Alternator fixed the problem.

Or, take it to A.A.P or A.Z. and have them check it.

 

[Kawiguy454]

Charging should be between 13.5 and 14.5 volts. use a multi meter to check.

 

[Dave Sherman]

Don't know if an '07 had the "smart" alternators, but from my '10 Traverse service manual it did say it was normal for the voltage to fluctuate. For example, turning on the headlights it purposely lowered the voltage to extend the bulb life. It also did not try to keep the battery 100% charged, so it could be as low as 12.5-12.6 volts and it could briefly be running off the battery alone. Might want to see if the service manual mentions anything like that.

 

[eljefino]

Did it just get warm down there? System voltage is reduced when it's hot to protect the battery.

Was it like this previous summers? Did you just start worrying about that gauge?

If the alternator were going out (but not gone), shedding load (lights, HVAC) or revving the engine should bring the gauge back up to its intended zone. Otherwise, it's working as expected.

 

[Silver]

What does an actual meter indicate the voltage to

12.72 truck off after sitting about 2 hours.
Cold start 15.45.
Slowly drops to 13's after about 7 minutes. Lights, ac will make the guage move a tiny bit but it doesn't drop.
Cut truck off, battery at 12.9.
Start again, back up to 15.45.

Apparently this truck does have "smart charging". It's just been so long since I drove it I wasn't sure if that was normal, and having the battery drained last week had me paranoid.

 

[meep]

The above is normal. It lowers charge voltage as it either measures or predicts the battery temperature is increasing. Cold batts need more voltage to charge.

 

[wtd]

The gauge on my 98 chevy K3500 reads about that most of the time and has for the 13 years I've owned it. I've had a couple of different alternators and a few batteries in it during this time and the gauge always reads the same so I'm assuming my gauge is not accurate anymore. My multimeter always reads higher than this gauge does.