The backup battery is the power source for the sbRIO9651s internal RTC and the precise RTC (ZSOM-Mini) when no other power is applied to the target.
The Backup battery is directly connected to the backup voltage input of the sbRIO9651
The Backup battery is optionally available as solderable add-on PCB
By default only the precise RTC is powered by the back up battery.
To power the sbRIO9651s internal RTC the zero ohm resistor highlighted in the picture below must be mounted: