Again I do not know which would be the easiest on your battery because I am never that dependent on my computer when mobile and hardly ever use it. But you may be asking for too much. The best I ever got out of a laptop battery “using it” was a couple hours unless it was sitting there asleep/hibernating. But if it is just going to sit I turn it off. So if you are getting more than three hours that is already incredible. I’m not sure in the real world I have ever heard of getting much more than that.
So I guess I can’t help much with that...
I've been on my laptop Huawei MATE D - AMD Ryzen 5 8mb RAM, stoc SSD drive and I've been online since 9am (so for 4 hours already) and when I hover over the battery this is what I see.
I know it's not exact or completely accurate but it's not far from what I end up getting before I put it back on the charger when it drops below 5%. Going by average, I'll get at least 10 hours easy.
This is in Windows 10 with anywhere from 5-10 tabs open in Vivaldi (at this moment I have 16 tabs open). If I try the same thing in Fedora 43 or Linux Mint XFCE I'm LUCKY to get 5 hours with similar usage. How is this possible? Less than half of the battery life with the 2 different versions of Linux I have used.
So much for the thought Linux is less resource heavy than WIN10.