I have a 7.5 year old Asus Zenbook UX305CA. It was the perfect laptop for my use case, given I run all heavy stuff on remote servers. 3200x1800 HiDPI screen, 8GB RAM, no fan, rigid aluminium construction (so it feels high quality), and it runs Linux pretty reliably. It used to get at least 6-7 hours of doing actual work, and one night I forgot to hibernate it or plug it in, and it was still running the next morning.

Now, 7.5 years later, the battery is not so healthy any more, and I'm looking around for something similar, and finding nothing. I'm seriously considering just replacing the battery. I'll be stuck with only 8GB RAM and an ancient CPU, but it still looks like the best option.

Another useful thing is that you can buy small portable battery packs that are meant for jump-starting car engines, and they have a 12V output (probably more like 14V), which could quite possibly be piped straight into the DC input of a laptop. My laptop asks for 19V, but it could probably cope with this.