I'm following this thread with interest, as my rides often take me to remote locations where a charging system failure would be highly problematic. I keep an eye on my battery voltage.
I have a Garmin 276c plugged into the GPS power plug near the battery and have configured 2 things on this unit.
1. one of the fields displays the voltage
2. one of the alarms is set to alert me to voltage falling below 12V
Normally I glance down while riding and see 13.7V +/- 0.1V regardless of the electrical loads I typically use. Occasionally, 2 or 3 times/day, I will notice a low voltage alarm and see a voltage of around 10V lasting for a second or two. Since I'm using CAN-bus supplied power from that plug, I've been wondering if this brief voltage drop is just part of the normal operation of the bike. It's not just turning off the power, since that would show the GPS internal battery which is around 7V.
Anyway, I thought I'd mention the GPS display and alarm capabilities in case others here have a Garmin hard-wired to their bike.