Apple finally revealed the ultra-thin iPhone Air, and if the specs are anything to go by, it’s a beauty: 5.6mm thin, a great display and the A19 Pro inside it. But the glossy intro skipped over the one thing that matters most in a device this slim: stamina. My biggest question had always been battery life, and Apple did not put that issue to bed.
Ultra-thin phones are a juggling act of aesthetics and physics. The iPhone Air shows you can shave millimeters and still bring the best tech, and it also seems to indicate you can’t cheat battery math without similarly felt trade-offs.
Why thin is still shorthand for short stamina
Battery capacity scales with volume. A slimmer housing also means less space to fit cells and thermal gear within, even when shaping the nooks and crannies for custom packs. And research often cited by IEEE Spectrum suggests lithium-ion energy density has been increasing single-digit percentagewise each year —great for incremental gains, but not enough to work miracles in a machine this thin.
At the same time, today’s phones take more of a power draw in actual use: brighter screens, higher peak brightness, always-on displays, complex camera pipelines and 5G radios that spike draw in weak-signal areas.
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There are efficiencies to be gained here and there, chips like the A19 Pro certainly, LTPO panels, but at this point those are evolutionary improvements banging against a hard limit — the dimensions of the cavity for the battery.
Apple fixes two, raises questions
On stage, Apple’s VP of hardware, John Ternus, crowed about “hardware and software” innovations that drive strong endurance. They’re just the poster child: consider Adaptive Power Mode in iOS 26. It smartly curtails performance and display output all day long. Translation: To get sturdy battery numbers, the phone wraps both throttles around how hard it runs and how bright it shines.
The second repair is more revealing. Apple released an accessory that is named iPhone Air MagSafe Battery—specifically designed for and specifically listed as compatible with only the iPhone Air. It’s rare to see a lead spec sheet that touts “video playback with iPhone Air MagSafe Battery,” essentially codifying an external pack as a piece of the endurance narrative. The attachment, sold as an add-on for the phone, costs an additional $99.
The numbers tell the old, familiar story
Apple claims the iPhone Air will have up to 27 hours of video playback. That’s three hours less than the iPhone 17 standard, and a full 12 hours behind the 17 Pro Max. Video playback is a best-case scenario metric for Apple—keeps the screen on continuously, efficiently decodes video—so being slower even there is interesting. In more demanding activities such as 5G hotspotting, navigation or camera use, the margin sometimes grows larger. Independent labs like Consumer Reports and DXOMARK have demonstrated over and over how real-world variables (signal quality, background activity, heat) can eat away at headline numbers.
It’s the same cautionary tale as rival ultra-slim devices such as the Galaxy S25 Edge. Several reviewers also reported uneven endurance in mixed-use cases, highlighting how thin design falls short once you move beyond controlled benchmarks and into mixed daily use.
Heat, performance and the actual day
Balancers are only half of the equation.
Thermals are the other half.
With less mass and less internal volume, there are fewer places for heat to go. However slim the 5.6mm body of the Note 20 won’t pack in a decently-sized heat spreader or a vapor chamber so easily, and not even the most efficient 3nm silicon is free from needing both to run at its best. When a phone gets warmened, it doesn’t just throttle performance; it can also subtly nudge power draw higher as radios and displays operate inside thermal constraints.
Which is why it concerns me that the dependence on Adaptive Power Mode is becoming so high. When a thin phone has to fall back on system-wide caps in order to get through a day, the experience ends up bending around the battery, not the other way around. It’s a tacit admission that the form factor — not your needs — is in control.
What would make me change my mind
There are ways forward. Stacked-cell designs, more aggressive silicon-anode chemistries, smarter thermal designs could recuperate meaningful capacity and stability without much extra thickness. Apple has traditionally been ahead with custom battery shapes, close integration of silicon and software, and obsessive power management. But the iPhone Air’s stance on that—throttle first, sell a separate battery pack second—feels like a capitulation to industrial design, not an innovation around it.
We will require some independent testing — DXOMARK for endurance suite, AnandTech for sustained-performance analysis and teardowns from iFixit — to see how the iPhone Air handles long 5G sessions, prolonged camera use and gaming. I’d be thrilled to be wrong. For now, the signs stand out: Apple made a stunningly thin phone then relied on software and an addendum to paper over the reality that reasonable battery life does not fit in a thin phone.
That’s not the answer I was looking for. The iPhone Air is a triumph of design, but my worst nightmare persists: for most people, battery still determines how you can use your day — unless you’re willing to pay to bring more of it along on the back.