Rohde & Schwarz SMH Error message

[Eddiee]

I have a problem with a Rohde & Schwarz SMH signal generator. the model is 845.4002.52. 100Khz - 2000Mhz.
I get a flashing statues LED and an error code 6.  The manual tells me that error code 6 refers to 'Battery level too Low'.
Where is the battery? I have opened the cabinet and there is no battery to be seen. Most of the circuit boards are inside screened cases which I am reluctant open!  I cant find a battery in the service manual - or any reference to a battery in the users manual.
Otherwise the generator sems to be working OK - but I havent checked all the functions.  Any help with this would be most gratefully welcomed.

Since this post I have solved the problem.
There is a battery inside the processor case which is located at the top front inside the unit. First remove the feet at the rear of the unit and then remove the top cover.  The processor case is seured with folding clips that are easy to operate. Once removed, the case is opened by removing the self-tapping screws on the component side. The battery is a half-size AA lithium Thionyl type ( RS Stock No. 436-4768 ). Simply unsolder the old battery and solder in the new one, taking care to observe correct polarity.

Eddiee