What kind of system are you running?
On my thinkpad, arch install squeezes 9 hours after 7 years of use.
On a dell XPS I'd get about 13 hours with the gpu disabled and display set to 1440p instead of 4k. Sure you might say "but I need my GPU and 4k 15'' display" to which I reply eh maybe but I don't.
I have a normal ubuntu install, I use the i3wm to reduce general load. Resolution set to 1440p with xrandr, no scale adjustments. GPU disabled, totally on intel graphics.
My xps is about 4.5 years old right now, I have replaced the battery when it started to swell slightly, the replacement was salvaged from another and even worse, so after a year I put the original battery back in.
I honestly think the biggest thing is a tiling wm. Any time I go from full gnome to i3wm, my battery life gets an instant 3 hour bonus.
Big ole note, because of the age and battery degradation, i can squeeze about 6-7 hours out of with if I limit myself to a single firefox window and text editors. When it was brand new, 13 hours of normal use was totally doable.
Mine's a 4th gen X1 carbon with an ancient Antergos install from 2016 that I converted to normal arch after they closed the project. i3wm, probably some thinkpad specific tweaks from the arch wiki but the machine is so damn stable I rarely think about it.
Definitely not physically possible in my bag. I've chalked it up to the fact that linux desktop environments are just a total hodgepodge of weird components with unclear responsibility boundaries that couldn't possibly handle all the edge cases properly when you stick them all together. This leads to stuff like the fact that if I suspend my laptop with an external monitor connected, but then un-suspend it without that external monitor connected, I'm often presented with a lock screen that I can't actually interact with, forcing me to either seek out a monitor or switch over to text console to log in and kill my session.