Good news, folks!
Yesterday I succeed on reading an dying cause of it respectable age DS1225Y from my TEK 2467B. As Mr. Hugo Holden noticed in his article, that this NVRAMs may get corrupted while reading attempt in programmer because of some programmer may sunk current from ICs pins, this may finish off already discharged heroic lithium battery inside DS1225 (mine is actually produces in mid 91, so it at least 23 years old with only 10 years guarantee data storage). I decided not to relay on chance and do a surgery for my DS1225Y and shunt it's internal battery with external fresh one before putting it to programmer. I spend some unpleasant hours desoldering it from A5 board, primary because if tiny traces and sucker back-kick. After DS1225 was desoldered, I replaced it with gold plated socket with round contacts and started the main act. Using Dremel with very small grinding bits I dig into compound on the bottom side of the DS1225 to reach DS1218 pin 7 shat is connected to internal battery positive terminal. Then, I tin going to install a standard CR2032 battery socket, salvaged from an old mother board. As I'm going to replace DS1225 with Ramtron 16W08 or STK12C08 (I got both, see what will do better), I decided to temporary stick socket on the top of DS1225 with a dual side sticky tape and then solder positive terminal to pin 7 of DS1218 and negative to pin 14 of DS1225. After battery was installed and wires soldered, I put DS1225 back again to see if it still holds calibration data. My scope booted without any warnings and EXERCISE 5 showed correct power hours and cycles. So, I put DS1225 to my new Wellon VP-390 programmer and successfully read data from it. Then, I just removed the battery and put DS1225 back again. I have no idea how to safely place external battery on A5 board, but now, as I have a dump, I don't really care.