I am literally getting Chromebook level battery life out of a machine that benches higher than the current i9 MBP 16. It is crazy. I am gobsmacked.
Admittedly I am coming from a 2015 rMBP as my previous daily driver. That has lost half its battery capacity according to CB and on Catalina even during light usage (literally just running Chrome and Music/Tidal) the max I'd get out of it is 1.5 hours.
So any new laptop would have been better than that old thing. But I also use a Chromebook and more recently my iPad Pro for travelling (Covid not withstanding). So I'm used to amazing battery on those.
The MBA is seriously better on battery than my Chromebook, almost on par with my iPad Pro (depending on what I'm doing with it), and just generally an all-round battery beast.
I can use this thing for a day straight running Chrome with 10-20 tabs, playing music through YouTube, Music, Tidal, or VLC, multiple messaging apps, my VPN client, and Little Snitch. I'll have 35-40% left by the end of the day with that usage.
This is especially impressive when half of that is running through Rosetta 2. I fully expect battery to get even better when all my daily apps are ported to native ARM.
I'm yet to give it a proper test when putting more load on the CPU, like using Logic Pro or iMovie, but I will be doing that very soon and I expect equally amazing results. I would not have even dared to open iMovie on the old MBP without it being plugged in. It'd die in 30 minutes. On this I have no worries.
Also curious to see how it fares with Transmission running in the background which is part of my regular use on the MBP but I can't do it on my MBA yet until 11.1 comes out due to a bug that causes Transmission to crash LS and potentially cause a kernel panic. It's been confirmed fixed in the 11.1 beta so just awaiting the official release.
Anyway, overall impressions are extremely positive. This is amazing stuff and it's only the first gen!