Infatti, basta semplicemente adoperare la chiave per aprire manualmente sia gli sportelli che il bagagliaio posteriore ove è collocata la batteria dell'auto, questo almeno nelle E34, E39 ed F01.
Ai fini dell'interruzione elettrica è indifferente. Ai fini della sicurezza si stacca il negativo perché a massa sul telaio e rimanendo collegato il rischio contatto è elevato, ma con isolamento certo del positivo si supera anche il problema sicurezza.
Secondo me consigliano di staccare prima il negativo perché normalmente non si utilizzano chiavi isolate per cui partendo dal positivo si può toccare il telaio facendo corto circuito, mentre partendo con il negativo non si corre nessuno rischio.
Concordo con @Bmw_pugliese per il distacco del terminale negativo Qui di seguito le indicazioni del TIS per la mia F21, i modelli precedenti potrebbero non richiedere certe cautele ma meglio sapere cosa e come fare le cose anche "semplici" come scollegare una batteria: Before disconnecting vehicle battery: Turn off the ignition and other electrical consumers/consumers to prevent sparking when reconnecting. Notice: If the ignition is not switched off when the vehicle battery is disconnected, fault memories may be set in some control units. Caution! There is a danger of mixing up battery cables: if the positive battery cable and battery earth lead are the same colour and you are in doubt, follow the polarity to the vehicle battery, then mark and cover the leads The on-board computer and clock may lose your data. General notes on disconnecting the vehicle battery: Do not disconnect battery leads and leads from alternator and starter motor while engine is running. If necessary, deactivate installed auxiliary batteries as per vehicle-specific repair instructions and disconnect if necessary. Cover battery negative terminal(s) and secure. Disconnect terminal of the negative battery cable from 12-V vehicle electrical system/vehicle battery only after successful and confirmed deactivation of any installed intelligent auxiliary batteries. Cover battery negative terminal(s) and secure. Disconnect both negative battery cables in the version with non-intelligent auxiliary battery. Cover battery negative terminal(s) and secure. When work is carried out on the electrical system, faults may be caused in the fault memories of some control units when the vehicle battery is connected. Only lead AGM battery: On vehicles with IBS at negative battery terminal: Do not under any circumstances pull/lever off pole shoes by force. Do not under any circumstances release the hexagon socket screw of the IBS. Note the following after having connected the vehicle battery: Caution! The scope of application of some systems may be restricted after an open circuit. Personal Profiles may also be lost. Settings or activations must be carried out, depending on the equipment specification. For example: Activate slide/tilt sunroof, if necessary Activate power window, if necessary Refer to the diagnosis system for further vehicle-specific information.
