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2012 Dodge Grand Caravan Voltage Wildly Fluctuates

I have a voltmeter plugged into the accessory port on my van. Yesterday the battery light came on, and I noticed the voltage was fluctuating quite a bit, from 14.7 down to below 11. The light went off, but has come on once since then. I’ve noticed that when the voltage is correct, revving the engine up to above 2500 rpm will cause the voltage to drop considerably.
Autozone says I need a new battery, that one of the cells is dead.
It IS the original battery, so it’s over 8 years old. But does this sound more like an alternator problem?
And if so, is the voltage regulator on the alternator, or is it in the main computer on this car, like I’ve read somewhere?

If you have a questionable battery, that’s the first thing that’s replaced whenever there’s an electrical problem in a vehicle.

I mean, everything electrical in the vehicle relies on that battery.

Tester

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OK , replace it and see if your problems go away . Most Auto Zone stores will change out your battery if you buy it there.

That battery has owed you nothing for at least a couple years.

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Sounds like a slipping belt to me…

Well, I installed a brand new battery this morning, and the problem just got worse. Now it’s not charging at all. Since I don’t relish the thought of changing an alternator in the driveway when it’s sleeting and snowing, I guess it’s off to the dealership tomorrow! On this particular vehicle, I think you have to disconnect the radiator hose which means draining out the coolant. Not a fun job in some freezing weather!

Don’t be surprised if you’re told the vehicle needs one of these.

Tester

Yeah, I won’t be surprised. I’ve had to replace the computer on a Dodge van in the past and it was about $1200.

Well, the dealership said the alternator was bad, AND when it went bad it over voltaged the main computer, so that had to be replaced as well. Total cost: $1900. Plus the cost of the new battery. The old one checked out fine at home, so I’ll just keep it as a spare.