It is not necessary to leave the ammeter inside the vehicle, or connected. The procedures are well established, and have been posted here previously.

First, put a jumper wire with alligator clips across the battery terminal and post. The remove the battery terminal. The jumper wire maintains the circuit. Now put the ammeter parallel to the jumper wire. Now remove one clip from the jumper wire, and the ammeter maintains the circuit. Bingo.

You have to manage the issue that opening the doors triggers things to come on.

After awhile, it will go to sleep.

And the shift light has no bearing on whether or not it is in sleep mode. BMW techs posting here have confirmed that multiple times. On some models yes, on others no. My 2003 kept the shift light on for four years. Never had a battery issue, despite leaving it in airports for up to 4 weeks.

Edit: BMW bulletin on shifter light, courtesy killcrap

http://www.xoutpost.com/692305-post24.html

Edit: Helpful thread. See post 42, with the link, for a step by step.

http://www.xoutpost.com/bmw-sav-foru...es-fast-2.html

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue