Patches and discussion for Ensoniq VFX family

Hi - new member here!

I was looking for detailed information on how to replace the battery on my VFX-SD1.  

1)  I went as far as opening the lid on the top of the keyboard, but I didn't see the battery 
- where would it be?  And, how would I get to it?

2) I understand that the battery is soldered to a circuit board (somewhere), but does 
anyone know what kind of battery it is, and who supplies it?  

Any help would greatly be appreciated.

Thanks!