If the battery has been disconnected, the taildoor glass will need to be recalibrated. If the alarm was armed when the battery was disconnected (or discharged), disarm the alarm after reconnection - the taildoor glass will fully lower. This will happen automatically if the alarm was in disarmed state when the battery was disconnected.
After battery reconnection, fully raise the taildoor glass (if the glass is not fully raised, an error 'beep' will sound) - the taildoor glass is now recalibrated.
This procedure is taken from the Land Rover Publication Pt No LRL0313ENG
06.99 Free Lander 1st Edition Copyright Rover Group Ltd 1999
Hope this is of help to you.