I have a 2017 Carrera S with about 600 miles on it. I have a feature on my radar detector that tells me when the battery voltage gets low.

During the drive home today during one of the automatic start stops at a light, it tripped the low battery warning.

The thing that concerns me is that they replaced the battery before I picked up the car. I am wondering if there is a further issue. I have between 11.8 and 12.1 volts with the key and lights on in the garage before I start it and around 14.3 while it is running. I was curious what you guys show in similar situations. Thanks.

 

same here with my built in passport.
After 5 years I purchased and installed a higher capacity battery and I stopped getting the auditory warning from the detector.

nothing is wrong with the car

you will also notice that the voltage is always higher when in Sport mode

 

The other thing I have noticed today is when the start/stop kicks in at a light the voltage drops to the point it has to restart itself before I pull my foot off the brake.

 

normal. exact same thing here. don't worry about it.

 

Gee, someone actually uses stop/start on their 911!!
For the miniscule amount of fuel savings, the hassle just isn't worth it IMHO.
Oh, and yes, your vehicle is operating within normal operating parameters.