I have done a full 8 hours of work on my Dell Latitude 5440 before on battery. I put it in bat saver and it lasted me the whole work day.
But I re cognize something: why would I need to do that?
I sat a desk or my couch all day both of which had a convenient outlet. There was no point in doing that all on bat. Yeah it's impressive to have a crazy long battery life and is why I wanta MacBook for coffee shop coding days, but again, there's almost guaranteed to be convenient outlets and I own a 145Watt battery bank if needed. Thus my $150 ThinkPad E495 has been reaching 16+ hours of use without needing a wall wart.
Maybe your use case is different but mine where I'm certainly going to be stationary enough to use a plug or a battery bank means I can't justify the apple tax. Plenty of people have done this calculation hence why Apple still doesn't have an appreciable enterprise market share let alone a competitive one.
It's insane. I really want one for that reason, but ThinkPad with a ugreen 145 Watt battery bank gives me 16 hours of use. That's all waking hours.
It's hard to justify spending 3x as much on a single laptop just for that kind of battery life.