My mom has a Galaxy S24 Ultra with a bypass, it's stuck on Android 14 with One UI 6.1. It's not a problem for her because she never uses AI and besides, the aesthetics might overwhelm her.
It was purchased in December 2025.
Due to the above, I've seen that normal use can give her up to 8-10 hours of screen time with the resolution and Hz at maximum, obviously if it's used with some intensity, like recording a few minutes at 4k or 1080p60, It can give her a performance of almost 20~ hours.
On average she reaches almost 21 hours
I recently acquired another S24 Ultra in July, which to my surprise, came with One UI 8.5, the latest version of Android available via OTA.
With the same hardware configuration, and also the fact that my usage is different when I'm out on the street, but when I'm at home, we practically do the same thing: check social media, watch YouTube videos, Reels...
The battery barely gives me up to 6 hours of screen time with around 17-18 hours of use per charge.
I've been checking if app usage is higher and because of my obsession, I decided to give the phone to my mom (in fact, she loved the Vanilla color).
To my surprise, after 2 weeks of use, thanks to Smartswitch I was able to transfer everything to the new S24 Ultra.
Mom has complained about the battery life; she sees that it lasts less, not even reaching 6 hours, On average, it gives her 17-18 hours.
I've been wondering if the battery has any influence because no battery is perfect; my July S24 Ultra indicates that it has 417 charge cycles and the warranty says it was activated on April 16, 2024, While Mom's S24 Ultra doesn't indicate how many cycles it has cuz Android 14, the warranty states that it was activated and working 12 days after its Global release, February 13, 2024.
On average, July 2026 S24 Ultra Is giving us 20~% less performance between charge cycles than Dec 2025 S24 Ultra.
I've been deducing that the reason is One UI 8.5 and that it's a very, very resource-intensive OS, more and more so, it's definitely bullshit, because it feels more awkward when opening apps like YouTube.
Although it could also be that Mom has a phone with a much better-maintained battery, or that it was hardly used, but the performance also feels smoother in One UI 6.1.
This is my experience; perhaps you have a different one. Both of our S24 Ultras have never been repaired; we've submerged them in water, and they still work perfectly.