Necessary preliminary tasks

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Remove right LUGGAGE COMPARTMENT TRIM PANEL
Remove BATTERY COVER
Disconnect BATTERY NEGATIVE LEAD
Remove DISTRIBUTION BOX
Remove BATTERY

Open cap (1) and release nut underneath.

Remove cable lug mounting from positive battery lead (2).

WARNING: Risk of short circuits!
When installing, ensure:

Correct screw connection
Correct seating of cable lug mounting on positive battery lead (2)
Tightening torque 61 12 1AZ .

Fig 1: Identifying Cap And Positive Battery Lead

Courtesy of BMW OF NORTH AMERICA, INC.