I have disconnected my battery many times. You will have to reset your seat memory and OBC stuff (like date, time, speed alert, etc.). I am pretty sure that all other memory stuff will persist.

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SOLD
2000 E38 750iL Highline Edition, Upgraded with the lastest 2006 X5 Electronics
MKIV Navigation, 16:9 Display, Bluetooth, TV/Video with Backup Camera, Sirius, and Aux Input