Apple’s first foldable iPhone Duo carries a combined battery capacity of 4,883mAh, a figure that surfaced in European regulatory filings after pre-orders opened rather than through Apple’s standard product specifications. For anyone sizing up the Duo against the Pro Max lineup, that number needs context: foldable hardware plays by different rules, and raw milliamp-hours only tell part of the story.
A Battery Built for a Hinge
Fitting a competitive battery inside a foldable device is an exercise in geometric compromise, and Apple’s approach splits the difference, literally.
Think of it like packing a suitcase with an awkward divider down the middle: you work with the space available on each side. Apple describes the result as an iPhone-first dual-battery design, with one cell on each side of the hinge.
Secondary reporting based on Apple’s regulatory documentation identifies one cell at 2,962mAh and a second at 1,921mAh. Together, those two cells reach the combined battery capacity of 4,883mAh.
Where the Duo Lands in Apple’s Battery Hierarchy
Within the current iPhone lineup, the Duo’s capacity is stronger than it might appear for a first-generation foldable.
Among the recent iPhone models compared, the Duo holds the third-largest battery, sitting behind the iPhone 18 Pro Max at 5,567mAh and the iPhone 17 Pro Max at 5,088mAh. The 18 Pro Max holds a 684mAh advantage over the Duo, roughly 14% more capacity.
Below the Duo, the numbers fall off noticeably. The iPhone 16 Pro Max trails by 198mAh at 4,685mAh, while the iPhone 18 Pro sits at 4,288mAh, the standard iPhone 17 at 3,692mAh, and the iPhone Air at 3,149mAh.
mAh Is Not the Whole Answer
The Duo’s two Apple-rated endurance figures, one per display, offer a clearer picture of how battery capacity and screen size interact.
Apple rates the Duo for up to 44 hours of video playback on its outer display and up to 31 hours on the larger inner display. That 13-hour gap between two screens on the same device illustrates why raw capacity cannot predict real-world endurance on its own.
The outer-display estimate nearly matches Apple’s rated 45 hours for the iPhone 18 Pro Max, despite the Duo carrying 684mAh less capacity. The larger unfolded inner display draws more power, which pulls that figure down to 31 hours.
Apple’s playback ratings are controlled estimates, not independent test results. Brightness levels, connectivity, active applications, and your display choice will all affect real-world endurance.
What This Means Before You Buy
Apple’s stated playback estimates suggest the outer display can deliver endurance close to a Pro Max, while heavier use of the unfolded inner screen will reduce that considerably. Those figures come from Apple’s own controlled testing and will vary with real usage conditions.
Note that the physical SIM and eSIM configurations of other comparison models can carry slightly different capacities. The iPhone Duo is reported as eSIM-only worldwide, so that caveat applies primarily when comparing it to regional variants of other iPhone models rather than to different Duo configurations.
