Apple's latest developer beta dropped a software clue that is hard to explain away: for the first time in the history of iPhone software, iOS 27 Beta 4 contains Battery Health strings written in the plural — referring not to "the battery in this iPhone" but to "the batteries in this iPhone." No shipping Apple product triggers any of these strings. The only plausible explanation is a device with two battery cells, and the only device on Apple's roadmap that requires two cells is the foldable iPhone Ultra expected to debut at Apple's September event, as reported by Macworld.

The discovery came from Macworld journalist Filipe Espósito, who dug into the Battery Health module of iOS 27 Beta 4 after Apple seeded the update to registered developers on July 20, 2026. The new strings join a growing body of foldable-related code that has appeared across every beta since the very first, in June. At this stage in the development cycle, with Apple's annual September hardware event weeks away, these strings are not an experiment. They are a preparation.

There is also a detail in those strings that the beta coverage has largely undersold: Apple's code does not just track two batteries — it authenticates them independently. One of the new Health strings warns that "one of the batteries could not be verified as a genuine Apple battery." That language mirrors the parts-verification system Apple introduced for single-cell iPhones through its Self Service Repair program, but with a critical difference. A device with two cells and per-cell authentication has two separate parts-pairing dependencies — meaning a buyer paying $1,999 for the iPhone Ultra may eventually face two distinct Apple-genuine requirements when either battery needs replacing, not one.

iOS 27 Has Been Building a Foldable Picture Since Beta One

The dual-battery strings did not arrive in a vacuum. The first iOS 27 developer beta, released June 8, 2026, already included references to fold states and hinge-angle detection — software capabilities that are meaningless on any flat-slab iPhone but essential for a device whose screen geometry changes every time the user opens or closes it. Those APIs allow iOS to know whether the device is fully closed, partially open, or completely unfolded, so the operating system can adapt layout, brightness, and multitasking accordingly.

Beta 4, released July 20, adds the battery layer. Together, the discoveries describe a device's fundamental architecture from the inside out: the software knows the physical fold state, it knows the hinge angle, it expects multiple connected displays, and it now manages two separate battery cells with individual health tracking and authentication. The cumulative picture is substantially more persuasive than any single string read in isolation.

Apple has a documented history of seeding beta code for hardware it has not yet announced. Face ID appeared in iOS code before iPhone X was public. Apple Watch functionality was visible in software before the product existed. Code this deep into a beta cycle — four developer builds in — is not throwaway. Engineers do not write Battery Health parsing logic, per-cell authentication flows, and user-visible error strings for hardware that is not shipping.

What the Battery Strings Actually Mean for Buyers

The specific strings Espósito found include: "The batteries in this iPhone are performing as expected," "The health of the batteries in this iPhone has significantly degraded," and "one of the batteries could not be verified as a genuine Apple battery," as confirmed by Macworld.

The third string carries the most practical weight. Apple's existing parts-verification system — introduced as part of the company's Self Service Repair initiative — displays a warning when a replacement component cannot be authenticated as a genuine Apple part. For a single-cell iPhone, that means one potential parts-pairing dependency per battery replacement. For the iPhone Ultra, the iOS 27 Beta 4 strings suggest each cell will be authenticated independently, potentially creating two separate requirements.

Whether that translates into a meaningful repair cost difference depends on whether Apple ultimately allows individual cell replacement (one cell at a time) or requires full dual-cell replacement as a unit. The strings as written — specifically the singular "one of the batteries" framing — suggest the system is at least capable of distinguishing between cells and isolating which one has failed. That is better than an opaque single-module replacement. Whether Apple's service pricing will reflect that granularity remains to be confirmed, as noted by iClarified.

How Does a Foldable iPhone Need Two Batteries?

The dual-cell design is not a novelty for book-style foldables — it is an engineering requirement. When a device folds in half along a vertical hinge, its internal chassis is divided into two distinct compartments. Placing a single battery that spans the hinge is structurally impractical: the hinge mechanism consumes space, the foldable stack requires flexible interconnects, and a monolithic cell would be subject to mechanical stress every time the device is opened or closed. The established solution is a dedicated cell in each half, connected by the power management IC, which aggregates their capacity and manages charge distribution.

Samsung, Google, and virtually every other maker of book-style foldables has used this architecture since the category matured. The Samsung Galaxy Z Fold 7 carries a 4,400mAh combined battery across two cells. The Google Pixel 10 Pro Fold delivers 5,015mAh.

For the iPhone Ultra, Apple's battery supplier registered two new cells with a regulatory authority in a Weibo post published July 10, 2026, according to 9to5Mac's report on the Digital Chat Station leak, citing the leaker known as Digital Chat Station, who has an established track record on Apple supply-chain intelligence. The cells carry rated capacities of 1,921mAh and 2,962mAh — combined, a minimum of 4,883mAh. The supply chain estimates the final marketed figure could land between 4,800mAh and 5,000mAh once production tolerances are finalized.

The asymmetry between the two cells — 1,921mAh vs. 2,962mAh — is almost certainly a direct consequence of the chassis design. The half of the device containing the hinge mechanism has less available internal volume than the display-dominant half, which is why the smaller cell occupies the hinge side. This is the same structural logic other foldable makers use, though the specific cell split varies by design.

One notable data point: earlier rumors had placed the iPhone Ultra's combined capacity somewhere between 5,400mAh and 5,800mAh. The regulatory filing's 4,883mAh figure is a meaningful downward revision. The most likely explanation is that Apple's final chassis dimensions — including the liquid metal hinge and dedicated vapor chamber cooling system — consumed more internal volume than earlier engineering estimates anticipated.

What the Rest of the iPhone Ultra Spec Picture Looks Like

Beyond the battery, the iPhone Ultra's expected specifications have been assembled from supply-chain leakers, analyst surveys, and regulatory filings across months of reporting.

The device is expected to fold open to an approximately 7.8-inch inner OLED display (some sources cite 7.7 inches; Apple has not confirmed) alongside a 5.5-inch exterior cover screen, making it effectively a pocket-sized iPad that closes to phone dimensions, according to Ming-Chi Kuo's supply-chain surveys. The inner display carries a 2,713×1,920 resolution and a 4:3 aspect ratio — identical to the iPad's — at 120Hz via LTPO. When unfolded, the device is expected to measure between 4.5mm and 4.8mm thick, narrower than even the iPhone Air. When closed, that figure roughly doubles to approximately 9–9.5mm.

The internal display — and the crease at its center — is the single most scrutinized aspect of any foldable. Apple has reportedly targeted a crease depth under 0.15mm, significantly shallower than the Samsung Galaxy Z Fold 7's approximately 0.7mm. The crease angle is under 2.5 degrees. That specification is achieved through a combination of ultra-thin glass (UTG, under 30 micrometers at the fold), a 3D-printed liquid metal hinge that also acts as a heat sink, and a flexible adhesive between display layers. Samsung Display received Apple's approval to begin module production of OLED panels for the device; the outer cover display reportedly uses Samsung's M16 OLED (natively 10-bit), while the inner display uses the M14.

Apple's A20 Pro chip powers the device — the same silicon expected in the iPhone 18 Pro — built on TSMC's N2 2nm process with 12GB of LPDDR5X RAM. The A20 Pro is projected to run approximately 20% more power-efficiently than its predecessor, which helps offset the battery capacity constraints imposed by the chassis.

One confirmed omission: Face ID will not be present. In its place, a side-mounted Touch ID sensor integrated into the power button provides biometric authentication. The engineering reason is straightforward: Face ID's TrueDepth camera array — dot projector, IR camera, flood illuminator — requires bezel space that an ultra-thin foldable design cannot spare. This marks the first iPhone without Face ID since the iPhone SE third generation in 2022.

Who Should Wait — and Who Will Be Waiting Anyway

Analyst Ming-Chi Kuo has long framed the iPhone Ultra's launch through the lens of the iPhone X rollout from 2017: announced at the September event alongside the standard lineup, but with pre-orders and availability held back until October and November respectively, per his supply-chain surveys. His supply-chain surveys found that fewer than one million units will be production-ready by the end of Q3, compared with 20–22 million iPhone 18 Pro and Pro Max units targeted for the same period. If you intend to buy one on launch day, "launch day" for the Ultra may not arrive until November.

Pricing is expected to start at $1,999 for the 256GB configuration, climbing from there with 512GB and 1TB options. That would make the iPhone Ultra Apple's most expensive iPhone by a wide margin. For context, a resale value analysis from SellCell projected that a $2,000 foldable iPhone could shed approximately $1,292 of its value within its first 12 months based on existing foldable depreciation trends. First-generation hardware always carries first-generation risk: if the hinge, crease, or display performance falls short of the specifications Apple has been building toward, the cost of that bet will be $1,999 plus however much the secondary market has moved by then.

For anyone not committed to the foldable category, the iPhone 18 Pro and iPhone 18 Pro Max remain the conventional flagship choice — both expected to launch at the September event and go on sale September 18, with none of the supply constraints affecting the Ultra.

What Else Is in iOS 27 Beta 4

The dual-battery discovery dominated coverage of Beta 4, but the update itself is substantive across the board. Apple resolved a depth-effect rendering bug introduced in Beta 3 that affected Siri's visual presentation when invoked from the Dynamic Island or via a Home Screen swipe. Siri also receives a new splash screen at those same entry points, introducing first-time users to the redesigned assistant's capabilities.

A new "Always Show Request" toggle in Accessibility settings displays a live transcription of whatever the user says to Siri — useful for accessibility purposes and for users in noisy environments. The Apple TV app gains an automatic next-episode download feature: enable it, and the app queues the next two episodes of whatever you are currently watching, deleting finished episodes as you go. Developers and videographers gain a new ProRes Log 2 recording format option in Camera Settings — the newer Log format retains more dynamic range data than Log for additional flexibility in color grading. Per-network Wi-Fi Assist toggles allow finer control over which saved networks can supplement a weak connection with cellular data. AirPods controls in Control Center have been redesigned, with Adaptive Audio settings now accessible directly from that interface.

One feature that did not survive: the wallpaper Notification Center animation introduced in Beta 3, which displayed a cutout of the user's wallpaper subject when swiping down, was removed without explanation in Beta 4.

Frequently Asked Questions

What do the dual-battery strings in iOS 27 Beta 4 actually prove?

The strings are strong evidence — not proof — that Apple is preparing iOS 27 to manage a device with two independent battery cells. Beta software regularly contains references to hardware features under development, and Apple engineers do not write per-cell Battery Health parsing logic, user-visible error strings, and per-cell authentication flows for hardware that is not in the pipeline. The cumulative weight of foldable-related code across all four betas — fold state detection, hinge angle APIs, multi-display references, and now dual-battery health management — makes the "dead code" explanation increasingly implausible, as Macworld's Filipe Espósito documented.

How does the iPhone Ultra's expected battery compare to other foldables?

Based on supply-chain regulatory filings, the iPhone Ultra's two cells are rated at 1,921mAh and 2,962mAh, for a combined minimum of 4,883mAh, per 9to5Mac's coverage of the Digital Chat Station leak. That puts it above the Samsung Galaxy Z Fold 7's 4,400mAh but below the Google Pixel 10 Pro Fold's 5,015mAh. The earlier, higher estimates of 5,400–5,800mAh appear not to have survived the final chassis design — the liquid metal hinge, vapor chamber cooling system, and ultra-thin 4.5mm target consumed more internal volume than earlier engineering estimates allowed for.

If one of the iPhone Ultra's batteries fails, will Apple require a separate replacement for each cell?

This is the unanswered question the Beta 4 strings raise directly. The code's "one of the batteries could not be verified as a genuine Apple battery" language implies the device's software can identify which cell is the problem — suggesting individual cell diagnostics are possible. Whether Apple's service program will actually allow single-cell replacement, or whether it will bundle both cells into a single service event, has not been confirmed. The practical concern is that the iPhone Ultra may carry two separate parts-pairing dependencies rather than one, which at a $1,999 starting price is a meaningful variable in the long-term cost of ownership, as iClarified noted in its Beta 4 analysis.

When will Apple officially announce the iPhone Ultra, and how soon can I buy one?

Apple's annual September hardware event is expected on approximately September 8–9, 2026, where the iPhone Ultra is anticipated to be announced alongside the iPhone 18 Pro lineup. However, analyst Ming-Chi Kuo projects Apple will have fewer than one million units ready by the end of Q3, making an immediate same-day purchase unlikely for most buyers, per his supply-chain surveys. Kuo's model — based on the iPhone X precedent — suggests pre-orders and availability may follow weeks or months after the September announcement. If you plan to order, pre-ordering as quickly as possible after the event opens is the most reliable way to minimize wait time.