If the main 12v battery has been replaced by a previous owner…they may have installed the smaller H8 battery instead of the larger H9 battery just to save money. So a visual is the only way to tell which one they installed.
If you have the dual battery setup…the aux battery is monitored by the PCU (power control unit). The PCU is located on the rear right side behind the cargo panels (look below the rear fuse box). See
N7 in the illustration below:
The auxiliary battery should be located in the engine bay…see
G6 in the illustration below:
The main battery is
G1 in the illustration below:
