One battery must remain on the dual battery PCB at all times. Replace the batteries one at a time.
Remove the clip  that holds the battery  to the dual battery PCB. Replace the removed battery . Install the clip  onto the replaced battery .
Repeat the instructions for the second battery .
Set the main circuit breaker to the ON position. Push [POWER ON].
If the machine data is lost, use the backup file you created in step 1. The document you used for backup instructions also explains how to reload the data.