not related to longer battery life per se, but suspend-then-hibernate is the number one improvement to my daily use. the laptop suspends normally and if not woken in an hour, it suspends to disk. upon wake it restores from the swap file/partition. zero battery drain when off, resume from hibernate is faster than cold boot. I can go days without a charger; the other day I’ve “woken” it after like 10 days and did a full system upgrade - the battery and everything else was how I left it. after I was done, just closed it and left it.
my laptop is my secondary workstation and it’s not rare that I don’t touch it for days. it sucks major balls when I have to urgently leave and find out it’s depleted.
with systemd-boot and a fast and seamless boot process, this is as close as it gets to stuff Macbooks had more than 10 years ago.