Hi, folks.
Some time ago I started my work on replacing NVSRAM (the DS1225) in my Tek2467B and ended with a success replacement with SIMTEK STK12C68. The STK12C68 is a fast SRAM with EEPROM and a schematics to store/restore data to/from EEPROM on power failure condition. It combines both infinity read/write cycles of SRAM and 100-year data retention in EEPROM without need of any external power (and that solves battery problem). As data stored to EEPROM only at power-off condition, this specs simply make STK12C68 lifetime grater then scope's.
The original idea belongs to Mr. Hugo Holden, who consulted me during my work. His fears goes to store operation, hi told me that hi was able to reproduce condition at witch scope failed to boot and data in STK12C68 corrupted after very fast unit switch on-off cycles. However, with my STK12C68 I was not able to reproduce that behavior in unit. I did a series of unit power no-off-on-off as fast, as I was able to kick power button and then varying time delays. But that didn't convince no me, neither Mr. Holden. So, he suggested another test that I performed: I powered STK12C68 from a function generator, varying both duty cycle (10%-90% for square wave) and frequency from 0 to a couple hundred Hertz (that will never happen in real life) and even under that test contents of STK12C68 remained intact. So, this NVSRAM confirmed it usability. It work perfect in my scope: everything stored correctly, front panel and all settings stored/restored during reboot perfectly. Even after power button kick test.
The IC requires an external cap to store energy for power off EEPROM store cycle. I use the smallest recommended value: 68 uF tantalum, bypassed by 0.1 ceramic one. Besides, I use 0.1 ceramic to bypass the IC itself and 10K resister between pin 27 and VCC as recommended in datasheet. Previously I replaced DS1225 with a round pin socket. My current "adapter" is just a wire soldered STK12C68 to two raws of pins inserted to socket and some caps and resister soldered to all this mess and covered by a tape so it will not short to cover. But that work grate for testing.
P.S. The programmer I use for all my memory operations is Vellon VP-380. And I did a quick test reading an aged DS1225 (mine is '91 production code) without external parallel battery - and I can confirm that this universal programmer can read this old NVSRAM secure without corrupting contents.