Multi-day battery life is finally here — and Apple and Samsung missed the memo

I can’t say I’m remotely surprised to see reports that the Apple iPhone Air and Samsung Galaxy S25 Edge are struggling for sales. Nor that their successors might never even see the light of day. While the idea of a super lightweight, perfectly pocketable powerhouse sounds good on paper, they’re just not the kind of devices most people want to buy. They’re prohibitively expensive to start with, though that hasn’t stopped booklet-style foldables from finding a sustainable niche. No, the real problem — the one we all saw coming — is their dreadful battery life. And yet, better battery life consistently tops consumer wishlist

On the other hand, we now have our first smartphones that are pushing in the opposite direction. The new OnePlus 15 and OPPO Find X9 Pro are part of a new wave of handsets featuring silicon-carbon infused batteries, offering enough capacity to last two days of solid use and perhaps even longer for some. And I bet you can guess which of those two categories has my attention.

For context, the OnePlus 15 packs a 7,300mAh battery, while the OPPO Find X9 Pro boasts 7,500mAh. That’s about 50% larger than mainstream flagships like the Galaxy S25 Ultra and iPhone 17 Pro Max, which have 5,000mAh and 5,088mAh cells, respectively. Compared to this year’s slimline phones, the gap is even starker. These new handsets offer more than double the battery capacity of the iPhone Air (3,149mAh) and nearly twice that of the S25 Edge (3,900mAh). Brands love to talk about optimization, but physics doesn’t lie — if you want multi-day battery life, the bigger power cell is going to win.

But don’t just take my word for it; have a look at the battery life metrics we record for every smartphone that passes through our lab.

It turns out that doubling the battery capacity actually results in more than double the battery life when comparing the Air against these two powerhouses. In everyday tasks like web browsing and photo capture, the iPhone Air performs terribly. Samsung’s Edge fares better, but even it struggles to make it through a full day, while the 7,000mAh flagships easily last two full days of heavy use. The result is hardly surprising, but the data makes clear just how much more screen-on time these giant batteries deliver compared to the ultra-slim fad.

You might think that a smaller battery could recharge faster and get you back on your feet sooner, but that’s not the case here either. The iPhone Air takes an agonizing 105 minutes to reach 100%, while the Edge manages it in about 65 minutes — still relatively slow. Meanwhile, despite having nearly double the capacity, the OnePlus 15 and OPPO Find X9 Pro go from empty to full in roughly 40 to 50 minutes.

Part of the problem is that Apple and Samsung haven’t invested in truly high-speed charging. The Edge, for example, is capped at just over 20W, compared to the 45W available to Samsung’s Ultra line. Once again, the ultra-thin form factor is to blame — these phones are simply too slim to dissipate the heat generated during faster charging.

Of course, no one is buying these thin phones for superb battery life or quick charging. Still, if Apple and Samsung hoped that future generations of their slimline models would achieve mainstream success, they overlooked a fundamental rule of mobile tech: no one wants to worry about their battery icon turning red before the day is over. A phone with a 7,300mAh battery essentially eliminates that anxiety for power users and brings more casual users closer to the golden age of multi-day battery life — reminiscent of the feature phone era.

The OnePlus 15 and OPPO Find X9 Pro aren’t perfect. The OnePlus, for instance, has enough downgrades to irk longtime fans who might hold off upgrading despite the massive battery. Still, there’s no denying we’re looking at the future of smartphones — and importantly, what starts today in 6.7-inch flagships will soon trickle down to smaller mainstream models and eventually mid-range phones. If anything, the benefits will really be felt once $799 six-inch handsets can rival the endurance of today’s Ultra and XL models.

If ultra-slim phones are ever to succeed, they’ll need to embrace this new battery technology. It’s been a constant source of bewilderment in the office that Samsung and Apple didn’t debut their own silicon–carbon batteries in the Edge and Air. In my opinion, that’s probably the chief reason these phones have been received so poorly by so many. Perhaps the ultra-slim idea will resurface with renewed vigor in a few years, but until then, I’ll be happily powering through my third day of use — thanks to my phone’s massive 7,500mAh battery.