Can the RTCC on a PIC® MCU without a VBAT run off a battery?
Yes, please refer to the "Compiled Tips ‘N Tricks Guide", specifically to these:
- TIP #7 Battery Backup for PIC® MCUs.
- TIP #16 Deep Sleep Mode. Another option is to use hardware RTCC devices which have battery switchover characteristics.
Please visit http://www.microchip.com/rtcc for more details.