CMOS batteries last a lot longer than a year. Unless the system has been unplugged for a long time, they should be good for several years. I’m sure there’s actual data out there somewhere.
But yeah, a lot of people think “oh I’ll just put a UPS on it”. They don’t consider that unless you get a really big UPS, they’re only good for very short outages, seconds or minutes, to bridge the gap between the outage and your generator coming on (or the mains power coming back if it was just a flicker).
Also, the batteries in them need to be replaced every 3-5 years.