Backup Battery

Disconnect the ground terminal from battery sensor. Ref. to BATTERY
Remove the data communication module. Ref. to DATA COMMUNICATION MODULE , REMOVAL, Data Communication Module.
Remove the backup battery.
1. Remove the screws, and then remove the battery cover.
  Preparation tool:
  
  TORX® T10
2. Disconnect the connector and remove the backup battery.
Fig 1: Identifying Backup Battery Cover Screws And Connector
Courtesy of SUBARU OF AMERICA, INC.