With the release of iOS 27 beta 4 today, eagle-eyed developers and journalists have uncovered code strings that point toward an unprecedented hardware feature for an upcoming iPhone model: multiple internal batteries. The discovery, first highlighted by Macworld, adds weight to rumors that Apple is preparing a foldable iPhone Ultra — a device that could redefine the company's mobile strategy.

The code references are explicit: one string reads “The batteries in this iPhone are performing as expected,” while another notes “the health of the batteries in this iPhone has significantly degraded.” These phrases are grouped alongside existing single-battery iPhone references, strongly suggesting Apple is testing firmware for a dual-battery configuration. This is a notable departure from the traditional single-cell design used in every iPhone since 2007.

Background on the iPhone Ultra and foldable rumors

Speculation about a premium iPhone model — sometimes called iPhone Ultra or iPhone Fold — has circulated for years. Earlier this month, Chinese leaker Digital Chat Station on Weibo claimed the foldable iPhone would include two separate batteries to balance the device's weight and power demands. Foldable smartphones from Samsung, Oppo, and Google already employ dual-cell setups, as the hinge mechanism and two displays require flexible internal layouts. Apple has been slower to embrace foldables, but internal patents and supply chain reports have repeatedly indicated a foldable iPhone is in development.

iOS 27 itself has been a treasure trove of Ultra-related clues. Previous betas included references to a device with multiple displays, a foldable hinge sensor, and a new “Ultra” branding in system frameworks. The multi-battery code found today is the strongest software evidence yet that the hardware is being finalized.

Battery capacities and regulatory filings

According to a regulatory filing uncovered by Macworld, the two batteries in the iPhone Ultra will have capacities of 1,921mAh and 2,962mAh respectively, for a total of 4,883mAh. This represents a significant increase over the iPhone 17 Pro Max's 4,422mAh battery (released in 2025) and aligns with the higher power draw of a foldable device, which typically needs to run a main display and a larger internal screen. The dual-cell approach also allows for optimized charging speeds: Apple could use two smaller cells that charge in parallel, reducing heat gain and potentially extending battery lifespan.

Why two batteries instead of one? In a foldable chassis, space is at a premium. By splitting the battery into two modules, Apple can place them on either side of the hinge, distributing weight evenly and avoiding a bulge. This design also enables a thinner overall profile — a key selling point for premium smartphones. The 4,883mAh total would put the Ultra ahead of the Samsung Galaxy Z Fold 6 (4,400mAh) and close to the upcoming Google Pixel Fold 2 rumored to have ~5,000mAh.

Implications for iOS and battery health reporting

The code strings in iOS 27 beta 4 indicate that the operating system will treat the two batteries as a single logical unit for health reporting — using plural “batteries” in the user-facing messages. This suggests Apple has developed a unified battery management system that balances charge levels and monitors degradation across both cells. Historically, iOS has only reported health for one battery; the new strings imply a refactored battery subsystem. Developers working with the beta have also found new APIs for reading multi-cell status, which app makers could use to display battery information in third-party interfaces.

Battery health monitoring is a sensitive topic for Apple, which has faced criticism over the years for battery performance issues. The dual-battery system would need to be carefully calibrated to ensure that both cells age evenly. Users of foldable phones often report uneven battery wear due to differential usage — for example, the display panel on one side may drain one cell faster. Apple's software is likely to include charge balancing algorithms similar to those used in its MacBooks with multi-cell configurations.

Historical context: Apple's battery journey

Apple has rarely used dual batteries in its mobile devices. The iPhone has always employed a single lithium-ion pack, with capacity gradually increasing over generations. The iPad, too, uses a single large battery in most models, though some MacBooks have multiple cells to achieve high watt-hours. In 2018, the iPhone XS Max introduced a two-cell battery design (two separate cells connected in series within a single package) for space efficiency, but that was still a single logical battery. True dual-physical battery configurations are common in foldable Android devices but are new territory for the iPhone.

Apple's move toward a foldable with dual batteries is partly driven by consumer demand for longer battery life and faster charging. The iPhone 17 series already supports 40W wired charging; a dual-cell design could theoretically accommodate even higher charging rates by splitting the current. Rumors suggest the Ultra will support 50W fast charging and 25W MagSafe wireless charging.

What this means for the release timeline

Apple typically holds its iPhone launch event in early September. Given that iOS 27 beta 4 includes explicit Ultra code, it is likely that the final version of iOS 27 will support the new device at launch. This timing aligns with previous reports that the foldable iPhone will be announced at the same event alongside the iPhone 18 lineup. The Ultra is expected to command a premium price — perhaps $2,299 or more — and sit above the Pro Max models as a halo product.

Other details remain unconfirmed: the exact screen size (rumored to be around 7.6 inches when unfolded), the hinge mechanism, and whether it will include an under-display camera. However, the multi-battery code is a strong indicator that the hardware is in mass production and that software support is nearly complete.

For developers, the beta provides an opportunity to test their apps on multi-battery hardware via the simulator, though physical testing will have to wait until the device ships. The code also hints at new power management settings, perhaps allowing users to switch to low-power mode that uses only one battery to conserve the other.

As the September launch approaches, more leaks are expected. But today's iOS 27 beta 4 discovery moves the Ultra from rumor to near-certainty. Apple's first foldable iPhone — with its pioneering dual-battery system — is poised to be the most ambitious iPhone redesign in over a decade.

Best iPhone accessories for the upcoming Ultra

• AirPods Pro 3 (now only $199, down from $249)
• MagSafe Car Mount for iPhone
• 10-year AirTag battery case
• 100W USB-C fast charging power adapter
• AirTag 2 (1-pack / 4-pack)

Source: 9to5Mac News