Technics KN1000 - keyboard memory no longer working

Technics KN1000 - keyboard memory no longer working.

This is about 35 years old, a few months ago the memory buttons no longer recalled what was set in them. I friend said it could have a battery for the memory that has probably died. We opened it up, but could not find any battery. Any help would be appreciated. Pics of the location of the battery (if there is one) would be greatly appreciated.
The owner (not me) is in his 90s and had been playing daily, but the lack of the memory has been a real frustration for him.

The Service Manual can be found here : https://share.google/images/4eTyLvQyPXGCXYD8X

Syntaur have a battery cover here : Technics SX-KN1000 Repair Parts and Accessories - Syntaur

Perhaps the cover will reveal a battery? Not familiar with this keyboard, but hope this helps.