I would invest in an M Macbook just for this reason, that battery life is insane even with wi-fi on, imagine no connectivity, should pass 15 hours.
That said, it's not out of box like a Macbook.
What processor do you have?
I'm almost never CPU constrained, so I tend to have everything idled down as much as possible.
Edit: and just for context, opening firefox and browsing the web right now has me at 9W.