How is CMOS RAM able to hold data even when the power is off?

CMOS is not RAM. While it is memory, unlike main system RAM, CMOS is very tiny and only holds the BiOS configuration, nothing else. RAM is made from transistors and capacitors, which must be recharged. CMOS is made from several transistors wired as flip flops. It only needs a tiny amount of power to hold its data, and that comes from a small battery. If you remove the battery, it will lose everything.