Love my old Casio CZ-101 but it does suffer from lack of memory with limited onboard storage which needs some rather heavy batteries to maintain and the cartridges never seemed to hold the memory for long either.
I came across an article on Vintage Synth Explorer where someone was discussing a modification to add an internal battery backup when someone posted this rather neat little gadget. Not exactly cheap being in excess of £125 but it does a great job.
Ordered form the US and very much a home project evidenced by the hobbyist plastic case and sticky labels but what it offers is great. Long term storage and come complete with over 2000+ sounds and even adds an arpeggiator!
Well worth the money