orion0517

Hello,

How accurate is the 991 car’s internal battery volt meter? Compared to using a handheld volt meter …,

thanks

IXLR8

You mean the voltmeter in the MFD?

Good enough for what it is needed for. I remember doing a comparison and thought I wrote it down. Anyway, good within 0.1V.
Anything digital is usually ± % plus 1 count.

Autobahnschreck

Confirm statement by IXLR8.
Checking the dashboard voltage indication with a high-accuracy calibrated 4 1/2 digit DVM (FLUKE) I always find it within the digital resolution limit.
The actual measurement accuracy probably is (and also should be) bettter than the 3 digits displayed.

asellus

+1 to "yes it's accurate" -- this question gets asked every now and again, and numerous people have tested the accuracy of their MFDs to confirm that they are accurate to within rounding errors.

To answer your probably followup question, yes, it's normal to see it up around 15 volts. AGMs have fairly high charging voltages, especially in low temperatures.