Some years ago I had a Technics organ, It was, as far as I can determine, the predecessor of the Technics keyboard line.
It used a capacitor to keep the memory alive (they claimed about three weeks). When the capacitor died, I replaced it with a 3.6 volt lithium battery. I put a diode in the positive lead of the battery so that it wouldn't be charged (and damaged) when the organ was turned on. When I sold the organ, six years later, the battery was still doing it's job and I had not lost a setting in six years.
Just a thought,
Walt