You folks have been more than helpful so far. However, VBAT doesn't just supply the back-up for the RTC, it powers up the entire board, quickly depleting the battery when you turn the normal supply off. 
This seems unusual to me as the typical development board (that has a built-in RTC) has VBAT just power up the RTC alone. I could instead use an external RTC as a workaround, but that seems silly.I am fully aware that I on the F446RE board, I need to move a jumper or two, or perhaps solder or unsolder one or more of the bridges. I have studied the schematics and I am puzzled as to which one of the cornucopia of jumpers and bridges to alter from their defaults. (There are quite a few!)
If possible, I would like to:
1) Isolate VBAT so I can connect a back-up coin cell for the RTC, and not have it simply power the entire board.
2) Be able to power the board (and peripheral 3.3 volt modules like the display) solely via 3.3 volts for normal operation, yet still be able to easily update the software via the USB on occasion when needed whithout changing the jumpers or solder bridges.
With the default jumper and solder bridge configuration, it seems you can't simply power the board up via the 3.3 volt (CN7 Pin #16). Not sure, but it won't boot up unless you power up via the USB first.
Once you have powered up via the USB, you can power Pin #16 and remove the USB power. I really love this development board. It is absolutely _awesome_ for my application. Hopefully, it will be awhile before you hear from this "pest" again.
Bill D.
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Reading the DS3231 spec sheet, and comparing to the STM32 RTC spec sheet, it looks like the DS3231 will keep more accurate time, for what it is worth...
Here is the link to the very helpful Nucleo 64 board manual where all this information can be found, (if you take the time to look 