Resetting Alarm system

Helppppppppppp, I have a 2000 7 Series BMW 3.5i, my problem is that I have used the car for 1 week, and the battery on the key has gone flat, opening the door with the key in the door lock sets off the alarm, and the only way that I can turn off the alarm is by diconnecting the battery, it sayas in the manual that by inserting the key in the ignition and turn to position 1 will reset the Alarm, this does not work, as I can start the car with alarm still going off, I have been told that I need to keep the key in the ignition with engine running which will then recharge the key and so allow me to de activate the alarm,

I there any body who has had a similar problem or can help many thanks