This model (and every other that I've seen, though, admittedly it's been a while since I've looked at a typical rack mount server) had an easily removed battery.
In machines of this age, I don't think anyone would have considered soldering something in like that. That didn't happen until halfway through the 2000s.
Not exactly a CMOS chip, but the Dallas Semiconductor DS1287[1] real-time clock chip had a built-in battery that was notorious for failing.