I already reached 19-20h, like leaving home at 7am and coming back at 3h with some 10% left.
Caveat: sometimes applications inhibit suspend so, for example, I know I can’t ever start Waydroid in such circumstances.
My battery is now old, but I can get 2h30 heavily using the Web, 4h using mostly normal applications (writing something, reading) and 12h idling without suspend sounds very plausible.
I can test and report over if of anyone’s interest. It depends a lot on any background tasks.
Usually, I slow charge my phone to 70% unless I am going to be the whole day out and I can spend the whole day out, take calls, distract myself while waiting for something - like a normal smartphone sans social crap, without fear. I just need to mind stuck background tasks, like Waydroid not going away when I stop it.