18 hours battery life is mostly marketing. Not even sure how to test that, maybe on 20% display brightness with no programs running, other than the OS...assuming it doesn't take screenlock/display off into account?
The question is, what's the battery life when you're doing kernel compiles or GPGPU.
And not to beat the already long dead horse any more, but toss in some electron apps running in the background, I probably average somewhere around ~7 hours or so. I'm not convinced the 10+ hour lifetime is possible if you've got stuff like Discord/Slack/VS Code open.
But in terms of when I am doing truly evil things to it, I am surprised it lasts as long as it does, be it max CPU compiling or all of this morning when I was toying around with stable diffusion, it gets around ~4 hours or so.