it is important for the Model 25 286 and 30 286 in addition to the 35SX/40SX and microchannel Model 55SX/LS (non-'486' submodels) and 65SX - all of the PS/2s that use the "Dallas" RTC modules: If you get commercial replacements, look for the keywords "114 bytes of NVRAM (or "user") storage. "113 bytes" mean a "Y2K-fixed" version with the "Century Byte" at offset 32h - it won't work in PS/2s ("The Undocumented PC" book says "microchannel models only", but empirically tested by me to show the ISA models are affected).
Packages that use the DS1285 (which is Y2K-fixed, and was in later PS/2s) with a replaceable CR2032 battery are fine...