In fact, I would recommend this particular 12V meter to every FFE owner--it's a nice looking addition to the car. When plugged into the main 12V outlet on the center console, it's positioned very nicely, and the red LED display is easily viewed from the driver's seat. What do you think the nominal battery voltage should be when parked and not charging? I'm just wondering what the minimum voltage required is to start the car. Mine is sitting at 12.8V right now.
Yep I can easily view the meter from outside the car looking in thru the window on either side.
In my garage I leave the driver side window rolled down and in OFF mode I can reach in press the start button a couple times and that turns on the 12v for less than a minute, long enough to read the meter for a quick check.
I'm getting 12.9V in OFF mode right after the car was in drive mode or remote start mode for 15min. In accessory mode I get ~13.3V and in drive mode I get ~14.5V. When the HV battery is being charged with my L2 EVSE plugged in, I get ~13.3V so its only doing a weak trickle charging in that mode. Full 12v battery charging only occurs in (ready to) drive mode, also in remote start mode, with the higher ~14.5V. I found setting remote start mode to use "last settings" for climate control and having climate control OFF when I turn off the car, allows me to issue a remote start (either via the FOB or website/smartphone app) which will charge the 12v battery for 15min without turning on the climate control system.
For mine, the voltage will gradually go down to 12.6V after a day in off mode and 12.3-12.4V if left in OFF mode for a few days. But perhaps my 12v battery is slightly weakened (due to being discharged a couple times this past month) so it would be good to hear results from others, perhaps your 12 battery might hold its voltage/charge longer than mine for days in OFF mode. Now that you have the easy to read meter installed, please post your results over a few days.
The couple times I had the 12v battery discharge issue, it wouldn't go into ready to drive mode below around 11V. It did start one time when it was down to ~11.8V. So I'm trying to monitor each day and always catch it if it gets down too low and before it goes below 12.0V, just doing a remote start for 15min once or twice will charge it pretty well if you don't drive it daily. If it gets down too low than an external 12v battery charger/jumper is good to have around for emergencies.