Profilux 3 and battery buffered clock

[FrankS]

I just purchased a used Profilux 3. I am very pleased with the purchase and plan to extend the unit with the purchase of additional accesssories for ATO etc.
However when I turn on the unit and set the clock up from my PC and save the setting everything is fine. When I pull the power cord from the Profilux and reboot (to simulate a power failure (testing)) the unit does not retain its clock settings. So the question- I have not opened the unit yet. I would assume there is a battery as there is reference to "battery buffered clock" in the literature. I have not been able to fine any information at the GHL forum or anywhere else in this regard.
Is there an internal battery? Can a user change it easily? If there is not a battery then does this behaviour represent a problem with the unit?
Thanks for your help.