How long has it been doing this since you replaced the battery?

When the nav loses power, it loses all of the tracking information it had about the satellite locations. It downlads a satellite "almanac" to help it acquire faster, and it loses the almanac with power loss. It can take 20 to 30 minutes, depending on how clear the view of the sky is, for it to reacquire the satellites and download the almanac.

As an aside, it uses wheel speed sensors, a compass, and an internal gyroscope to continue dead reakoning navigation when it can not see satellites. That is why it appears to be tracking OK.

There is a navigation service menu you can look to see what is going on. Select the "SET" menu from the main menu, and then immediately click and hold hte "MENU" button for about 10 to 12 seconds. The navigation service menu will pop up. Report back what you see under the GPS SENSOR CHECK and GPS sub menus.

__________________
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