The battery in my fr965 (FW 25.04) is down from 50% to 4% in 12 hours (while mostly sleeping, no activity). This never happened to me, usually I get about 5 days from 100%.
I don't know if it's a coincidence but yesterday my kids asked why their watch blinks green and mine red, so I disabled PulseOX entirely (which probably should've increased battery life, or at least not decreased it)
The only other change I made yesterday was to switch from one of the built-in watch faces to BIG EASY, which I user earlier for more than a year. (I changed from BIG EASY to the built-in in hopes of getting significantly more battery life before a 1 week bike tour, but there was no significant change, so now I changed back)