These battery backed SRAM and clock modules have a shelf life of 10 years, mine are at 17 years and still working as luck would have it! but if the SRAM fails you loose all installed options.
http://www.mcamafia.de/mcapage0/dsrework.htm
http://www.walshcomptech.com/ps2/dallasrework.html
http://www.ko4bb.com/manuals/index.php?dir=Tektronix/Tektronix_-_TDS784_TDS794_Digital_Phosphore_Oscilloscope