Update to the previous post:
I had my battery replaced under warranty a couple months ago, I wasn't seeing any practical issue but the Jebsen was showing as low as 10.9v on startup for a few secs, until it rose to 13-14v. Actual voltmeter readings were only ~12 v at the battery terminals.
Anyway, the readings while driving above using the Jebsen all show similar but a few tenths of a Volt higher with the newer battery; 14.1v is now mid-14v...