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Discussion Starter #1
Just had a battery go bad. Easy enough fix, now I'm obsessed watching the voltage on the dash dance from 12v to 14v all day long. Dealer checked it out and says it is fine. But I think it should be the charging system not doing something right or the gauge is not showing the correct voltage. Left the dealer it was at 13.5v for a while and then hit 12.5 for a minute, then 13v for a while.

Anyone notice their voltage moving around while driving?
TIA
 

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The gauges are not known for being super accurate. Take a voltmeter and hook it up to the battery, car off should be at least 12.5V. Start it up, voltage at idle should be 13.5.-14.0 V. Now turn everything on, AC, high fan, lights on high beam, RW defroster, Wipers etc. Run engine at 2000 RPM, should maintain ~13.5 volts. If it varies, could be bad diode/s or regulator.
Also, sometimes a new battery can be bad or not fully charged. I always charge a new battery for 30 [email protected] 10 amps and then check the voltage, should carry a surface charge to ~12.8 volts. Good luck.
 

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The voltage supplied from the alternator is controlled by the ECM.
Many things affect this, including engine RPM and ambient temperature.
It is normal for the voltage to vary.


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Perfectly normal; it's called BMS, or Battery Management System. You can turn it off with FORScan, if you want, but it saves fuel/power, since the alternator only charges the battery when it needs to, and on deceleration.
 
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Discussion Starter #5
Thanks for the replies. I did finally get a response back from the dealer. They essentially said the same thing about the BMS. That's a neat feature.
 
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