Q: I have a 2016 3.6-liter Cadillac with 18,000 miles. Lately, I’ve noticed that the voltage starts out at around 13-plus volts and works its way up to a little over 15 volts. It will lower a bit at stop lights. I'm experiencing no problems, but this seems to be something to check out. The car comes with an AGM battery, and I verified the dash reading matched my voltmeter. Older GM cars had a voltage regulator in the alternator, but I'm reading that some cars have the ECM control voltage. I don't want to start throwing new parts at it before I find what's causing this.
W.T., Rolling Meadows, Illinois
A: Historically, alternator output has topped out around 14.7 volts. That was before computer systems, which now maintain a close watch on power demand. It is normal for output to vary and to go as high as 15 volts to keep the battery at optimum levels. AGM (absorbed glass mat) batteries often need a bit more charging oomph than typical lead-acid batteries with plates. Save your money. You may need it due to inflation.
