General notes on disconnecting battery:

Do not disconnect battery leads and leads from alternator and starter motor while engine is running.
Cars with IBS on battery negative terminal:
Do not under any circumstances pull/lever off pole shoes by force.
Do not under any circumstances release socket-head cap screw of IBS.
Detach terminal of battery negative lead from car battery and second battery if fitted. Cover battery negative terminal(s) and secure. Refer to 61 20 900 DISCONNECTING AND CONNECTING BATTERY NEGATIVE LEAD .
When work is carried out on the electrical system, faults may be caused in the fault memories of some control units when the battery is connected.
When fitting terminal for battery negative lead: Tightening torque 61 21 1AZ .