Please note that dirt on the connectors (both on the phone and on the charger) will result in the phone constantly saying that it needs to be charged. A well known problem with the BeoCom 2.
If the battery is dead, simply unscrew the to screws at the bottom of the handset - the battery is held in place by a lock ring, B&O uses a special tool to remove this and I have not tried to remove the battery without this. But you could have a look.
Roger