Sony DVD Hard Drive recorder

[Barwell]

I have a Sony HXD970 hard drive recorder. When the recorder is switched off it loses it's memory, including the 'guide'. I can re-tune it ok but when it's switched off and on again, the guide and any TV programmes due to be recorded have disappeared. I'm guessing it's the back-up battery but don't know how to replace it. Has anyone else had this problem?