My reading of the manual says no battery. As long as the thing is powered on or in standby, the memory is retained. Toggle the front panel switch to reset or
physically disconnect and reconnect the power cord and the memories are all lost - in fact, they are all set to the default 100 MHz, -127 dbm setting.
The fact that the fan can remain on in standby was quite a nuisance to a lot of people. I think HP corrected this in the "B" version.