Batteries in BT Advanced digital home phone need to be replaced

[Apache060]

Hello,

I have a BT Advanced Digital Home phone with HD calling Type A,  I need to change the batteries in the phone as the the batteries Have had it, but I cannot get the back cover off to change the batteries.

Any help would be appropriated 

Thanks

[gg30340]

See page 18 of the user guide.

BT-Advanced-Digital-Home-Phone-User-Guide.pdf