Owner's Manual for the vehicle. With a quick reference ... - E38.org

Battery
175n
If you plan to store the vehicle for
longer than 4 weeks, disconnect the
battery from the vehicle electrical system
by disconnecting the cable at the
negative terminal.
If you intend to store your car for longer
than six weeks: Remove the battery,
charge it and store it in a cool (but frostfree)
room. After a period not exceeding
6 months and before reinstalling the
battery, have it recharged. If it is not recharged,
it will not be serviceable. Every
time the battery is discharged, especially
over extended periods, its
service life is reduced.
Avoid environmental pollution
when disposing of old batteries.<
Return used batteries to a recycling
point or to your authorized
BMW center. Maintain the battery in an
upright position for transport and storage.
Secure the battery against tilting in
transit.<
Removal and installation
Do not disconnect the battery
when the engine is running. Disconnecting
the battery cable when the
engine is running will cause a voltage
surge that will damage the vehicle's onboard
electronics.
Do not make any modifications in the
wires to the positive terminal. If you do
so, the protective function of the safety
battery terminal is no longer ensured.
Repairs and disposal may only be performed
by specially-trained personnel.<
BMW 750iL: Please contact your authorized
BMW center for additional information.
380de653
BMW 740i/L: When removing the battery,
disconnect the negative terminal
first, then the positive terminal.
Unscrew the battery retaining clamp
(arrow).
When installing the battery, connect the
positive terminal first, then connect the
negative terminal.
When installing a battery, be sure
that it is mounted properly. If the
battery is not mounted properly, it will
not be adequately secured in case of an
accident.<
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