Voltmeter in car acting up

So on our trek to the cabins the voltmeter descended to 13 volts and stayed there. At a stoplight it crept back up again then driving speeds crept back gown again. Restarted after filling with gas, was fine but driving away it crept down to again. Drive through in gear crept back up again, on the highway crept back down.Starts creeping down before going into overdrive. Coasting in neutral, no change. Got to our destination reading was 13. Stopped and restarted the engine, normal. 2017 Acadia limited 3.6 vvt, 30k miles…
I suppose a voltage display for the power point step 1

My first test if I had that problem, I’d use a DVM to verify the dashboard display matches a direct DVM measurement on the battery. If the DVM matches the dashboard display, second is a battery test, esp if the battery is over 4 years old.

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Battery was replaced, Jan or so ignition off as in engine not running reading is this hard to figure voltage for me… No dvm at the moment.

I understand completely. You’d think the marks would be either 1 volt or 1/2 volt increments. But those marks on your dashboard have little to no relationship to any sort of voltage scale I’ve ever seen … lol … about all I can say is best of luck.

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At least you can get some sort of Idea of what is going on compared to one with a idiot light with no gauge.

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No idiot lights went off!

What I meant was one like my wife’s car the only gauge it has is the fuel gauge.

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I hear you!

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Is this new behavior?
It might be a “smart” charging system that reduces voltage to save gas.
That’s what my 2017 Tucson does.
Sometimes voltage drops to 12.6V.
More about it here:

You can get one of these for comparison:

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Interesting thought. 'll check with the dealer. I can certainly hope it is by design. I’ll check with the dealer Monday!

Sounds perfectly normal. Modern day GM cars with AGM batteries control charging output to maintain the battery efficiently. AGMs don’t like or need a constant 14.4 volts when the engine is running. Can you toggle through your Driver Info Center display to have it display system voltage?

My wife drives a 2018 Cadillac and I can be driving down the highway at 70mph and see the system voltage go to 12.4 volts for periods of time.

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Adaptive charging systems have been around since the 1980’s. Charge the battery at 15 volts after start up on a very cold day, 13.0 volts on a hot day.

Charging close to 12.6 volts is best for the battery, charging at 14.5 volts on a 12 hour trip will age the battery faster.

A decade ago manufactures began using extreme measures to save fuel, reduce charging voltage to minimum while accelerating or cruising, then increasing voltage while deaccelerating to capture some of the energy wasted while braking.

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Dealer confirmed all is normal, surprising it never happened before, maybe it kicked in as the new battery in Jan. required programming to keep auto start working. My regular guy was saying he had to buy the battery from the dealer then program it, figured might just as well let the dealer do it, downside 630 cca. First long road trip since then. Blood pressure down, life is good!

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