The best battery life I ever got on a smartphone was on a HTC One X back in 2013 or so. It had a custom ROM (Paranoid Android IIRC) where I stripped out all the google services, blocked all wakelocks and so on. It had an nvidia Tegra3 CPU, which had 4 normal ARM cores and a 5th tiny core that ran at 100Mhz or so max (with powersave governor). On that setup, when I was not using it, it drained like 2% battery a day (50 day runtime). Since then we went from 40nm to 3nm, 2000mAh to 5000mAh, I'm doing the same things on my phone and yet, due to bloat and spyware the battery life is worse and worse. I went through HTC One m8, HTC 10, OnePlus 7Pro, and a Samsung Fold7 and each had worse efficiency than that 2011 CPU on the OneX (And a Nexus7-2012 until it died due to low quality NAND)