Yep, I'm with you here.
I mean, kinda, to a degree? Sure, a fully updated install of the launch version on an older iPhone will plausibly be easier on a battery than the latest revision. I don't buy a 50% runtime loss though. I'm not saying you didn't see that, I am saying that is not a universal truth, and is likely an outlier. I would expect the actual difference to be much smaller. If an analysis were done on a thousand old iPhones, I would expect the overall difference to actually be fairly small.
But people repeatedly mention that battery life plummets on older devices and there’s nothing that can be done. And also… an objective analysis done how?
Batteries cannot withstand anywhere near the maximum load of a device. I’m going to deviate to Bluetooth speakers, as I said earlier. My brand new speaker: rated for 24 hours of battery life at 44% volume, and 5 hours at full volume. I matched those numbers upon testing (and got 40 hours at 30% volume). The same thing happens with iOS devices: batteries cannot withstand a full load because it is too taxing. That’s why I dismissed previous messages saying I should run geekbench on both. Geekbench will obliterate the battery on both, and in that case, sure, they’ll be rather close, or the one on iOS 10 may not be able to withstand it.
Taxing the battery as hard as the device goes kills everything, so that use case is irrelevant in my opinion. How can you assess software impact if you just overpower the battery itself? You can’t assess efficiency if you’re doing the equivalent of hitting the battery with a heavy mallet. And that was my problem: I’m somebody who can optimise iOS devices enough - and has a light enough usage pattern - to get very long runtimes. With the updated 6s, I was failing. There was no light usage pattern that helped, it was just awful. With fairly low brightness (say, 30%) and cellular, and light apps like web browsing, I was getting 2.5 hours to 30%. With Wi-Fi numbers were slightly better, but still awful.
So an old battery doesn't perform like a new one, but you're happy with the compromises required to keep old ones optimised. I actually admire that!
But there are no compromises! With everything but the heaviest usage patterns (and this is an assumption, as I haven’t tested gaming that heavily), the device is unaffected. Like I said, high brightness, outdoors, camera use, cellular. That’s a heavy usage pattern. Battery life was unaffected. What more can I need?
I dont't buy the notion that an 11 year old phone will have unchanged battery life if you never update it. Physics and chemistry are real. I find it akin to the fuel-saver devices you plug in to your car's cigarette lighter, or the mythical "100mpg carburettors" I used to read about. You can't ignore chemistry. You can make compromises to maximise a battery's useful life, but an old battery is an old battery.
Please don't misunderstand me, I'm not trying to be insulting with these comparisons, they just illustrate my point.
I'm super happy with iOS 26.5 on my iPhone 14.
I assume there is indeed a limit. All I’m saying is that with original iOS versions, I haven’t found it yet. And it is arguably irrelevant for the context of this discussion.
Keep in mind that we are talking about an iPhone that is pretty much not used as a main device anymore (or as secondary either). You just need enough battery life to get you through a certain amount of years in which you use a specific iPhone as your phone, and that’s it. Then it doesn’t matter anymore. I can use the 6s on iOS 13 even with its poor battery life to play music and in that context battery life is good enough. It needs a recharge far faster than any other device I have when used for that purpose, but it doesn’t matter as much.
I have a seven-year-old iPhone Xʀ on iOS 12 with 89% health that I use for music. I will need a quintillion years to see any health-related impact because I don’t push it at all and I don’t even cycle it that much. But it’s only as good because it runs iOS 12.
I even have a 76% health iPhone 8 with 2300 cycles that I also use for music, and it’s fine, still like-new, but the point is, with an original iOS version, I render battery longevity irrelevant because the battery outlasts the original version’s compatibility. Why do you think I’m so harsh towards developers? Because the bottleneck for longevity aren’t batteries (which I could even replace if they were), but developers removing compatibility.
2300 cycles and it’s fine! (With 76% health). How much more do you need? In fact, I argue that the only reason why people replace batteries is because they are updated, and you get into the endless game of “if an iPhone with 100% health can barely withstand the load, one with 80% collapses, so battery health is relevant”. Yeah, sure, whatever, but whose fault is that? The battery or the iOS version? Funnily enough… I saw somebody who was still using an iPhone 6s. They had gone through SEVEN battery replacements. Are you kidding me? I’ve done zero and I’m fine. What you mean seven? I obviously fault iOS 15, which I know for a fact that it’s just too taxing. Even after battery replacements people report that it’s still garbage. A bit more stable because it can somewhat withstand iOS 15’s awful load, but battery life itself is garbage.
My argument is that the compromises you mention are almost theoretical. If, to see an impact on an original iOS version with a degraded battery that’s 20 years old and has 4000 cycles, you need to play Infinity Blade at full brightness… well, then that’s not much of a compromise then, is it? The device’s usability is long gone. And more importantly, the device’s relevance is also gone.