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      Does Limiting an iPhone's Battery Charging to 80% Increase Lifespan?

   Adam Engst

   Thanks to Juli Clover of MacRumors for her year-long experiment to test
   whether preventing an iPhone 15 Pro Max from charging above 80% would
   increase battery longevity. With the iPhone 15 line,[1]Apple added a
   feature that allows users to prevent their iPhones from charging over a
   certain percentage. Clover locked the maximum charge at 80% for the
   past year and has now [2]reported her findings:

     My 'iPhone 15' Pro Max battery level is currently at 94 percent with
     299 cycles. For a lot of 2024, my battery level stayed above 97
     percent, but it started dropping more rapidly over the last couple
     of months.

   How much difference did it make? Several of her colleagues at MacRumors
   with the same iPhone model who charged normally reported slightly lower
   capacity numbers (87% for 329 cycles and 90% for 271 cycles),
   suggesting that limiting the maximum charge provided a slight benefit.

   (Generally speaking, the more cycles a battery has experienced, the
   lower its maximum capacity. For reference, Apple defines a charge cycle
   as using an amount that represents 100% of your battery's capacity,
   regardless of how it's used over time.)

   Curious, I checked Settings > Battery > Battery Health on my iPhone 15
   Pro, too, and [3]Glenn Fleishman, [4]Nick Heer, and [5]John Gruber have
   also reported the following capacities on iPhone 15 Pros with normal
   charging:
     * John Gruber: 89% with 344 cycles
     * Glenn Fleishman: 91% with 411 cycles
     * Adam Engst: 92% with 346 cycles
     * Nick Heer: 95% with 273 cycles

   This anecdotal data suggests that the impact of limiting the maximum
   charge to 80% may be minor over a one-year period. It's possible that
   the benefit would be seen only after two or three years, when the
   iPhone might otherwise need a battery replacement. Apple presumably has
   better data that suggests that limiting maximum charge might be worth
   considering for those prioritizing battery longevity over convenience.

   The problem with drawing conclusions about battery longevity is that
   it's a [6]multi-variable scenario. A few that come to mind include:
     * Batteries are analog chemical systems, so no two batteries will be
       identical.
     * Heat is a major contributor to battery degradation, so leaving an
       iPhone in a hot car while at the beach can speed up this process.
     * The charging method may play a role, partly because wireless
       charging generates more heat. For instance, Juli Clover's charging
       was roughly 70/30 split between wired USB-C charging and wireless
       MagSafe charging, whereas the majority of my iPhone 15 Pro's
       charging was via MagSafe (see '[7]Going All in on MagSafe for the
       iPhone in the Office, Bedroom, and Car,' 6 May 2024). If you're
       concerned about battery longevity, favor wired charging when
       possible.
     * Charging habits affect battery longevity. The existence of the
       maximum charging and Optimized Battery Charging options highlights
       the extent to which lithium-ion batteries don't like being charged
       to 100% and held there. They also don't like being completely
       discharged, so try to avoid that.

   If you believe intentionally forgoing the top 20% of an iPhone's charge
   could be awkward, you aren't wrong.

     I left my 'iPhone' at that 80 percent limit and at no point turned
     the setting off or tweaked it. There were some days when I ran out
     of battery because I was without a charger for most of the day, and
     there were other times that I had to bring a battery along to make
     sure I didn't run out of power. It wasn't always convenient to keep
     it at 80 percent, but there were days when it didn't have too much
     of an impact.

   My takeaway is that it's seldom worth trying to outthink what Apple has
   done in iOS to optimize battery charging. For users who prefer
   convenience without sacrificing much battery longevity, Optimized
   Battery Charging automatically holds the charge at 80% and finishes
   only when necessary, making it a good alternative to locking the
   maximum charge at 80%. Turn it on in Settings > Battery > Charging.

References

   Visible links
   1. https://support.apple.com/108055
   2. https://www.macrumors.com/2024/09/24/iphone-80-percent-charging-test/
   3. https://twit.social/@glennf/113195036691578150
   4. https://pxlnv.com/linklog/80-percent-charging-limit/
   5. https://daringfireball.net/linked/2024/09/24/clover-iphone-15-battery-limit
   6. https://support.apple.com/101575
   7. https://tidbits.com/2024/05/06/going-all-in-on-magsafe-for-the-iphone-in-the-office-bedroom-and-car/

   Hidden links:
   8. https://tidbits.com/uploads/2024/09/iPhone-15-Pro-battery-capacity-scaled.jpg

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