RTC consumes absurdly small amount of juice, about 350 nanoamps, and is hooked directly to battery, bypassing any voltage regulation chips, so yeah. Also, I suspect there is a super cap providing a few hours of juice in case there is no battery. But I can’t be sure - the published schematics do not say what the value and model of C4051 are. Might as well be yet another voltage noise sink.
Does the RTC reset when you remove battery for like several seconds and then replace it again?
RTC can run with voltage as low as 1.0V. Flat battery provides more than 3V. Given the absurdly small current appetite of the RTC, comparable to leakage currents of diodes and capacitors, I’d say the battery can supply enough juice until it ceases to be a battery at all. This can take indefinitely long. More than few hundred years at the very least.