Here is a video on how to re-syn your key when you change the battery.[video=youtube;O-TI1jc_nbA]http://www.youtube.com/watch?v=O-TI1jc_nbA[/video]here is a video on how to change your battery for your E39 key.[video=youtube;KfAx7WK4dec]http://www.youtube.com/watch?v=KfAx7WK4dec[/video]