Quick Answer
iPhone Duo narrowly beat iPhone 18 Pro Max in Mediastorm’s two-hour video-recording battery test.
Battery remaining after recording: Duo 61%, Pro Max 59%, Pro 45%.
After three hours of 16:9 video playback, the order reversed: Pro Max 93%, Pro 87%, Duo 84%.
The Duo’s camera interface leaves large black areas on the inner screen, helping explain its surprisingly strong recording result.
For long video-watching sessions, Pro Max has the advantage; for filming, Duo performed much better than its large display might suggest.
What did the iPhone Duo battery test compare?
Recording a video and watching one produced different winners. In Mediastorm’s iPhone Duo deep review, the team compared iPhone Duo, iPhone 18 Pro Max and iPhone 18 Pro in two tasks: two hours of continuous recording and three hours of 16:9 video playback.
The interesting part is how the Duo moved from first to last between those tasks. Its battery performance is closely tied to how much of the folding display is actively showing content.
Two hours of video recording: iPhone Duo finishes first
The Duo finished the recording session with 61% battery remaining, just ahead of the iPhone 18 Pro Max at 59%. The smaller iPhone 18 Pro ended at 45%.
iPhone Duo
61%
Battery remaining
iPhone 18 Pro Max
59%
Battery remaining
iPhone 18 Pro
45%
Battery remaining
That gives the Duo a 2-percentage-point lead over Pro Max and a much larger 16-point lead over Pro. The surprise is how closely the foldable holds up against the biggest Pro model while keeping a much larger screen open.
Look at the camera interfaces below. On the Duo, a substantial part of the inner display is black. The viewfinder is not filling the entire panel, so the phone is not driving a bright, moving image across its whole folding screen.
For someone filming a school event, a trip or a long performance, this is encouraging: the Duo kept more than half its battery after the two-hour recording session. If you also shoot a lot of footage, our iPhone Duo storage guide covers the next practical question: where to keep it all.
Three hours of video playback: iPhone 18 Pro Max pulls ahead
Switch to watching 16:9 video for three hours, and the Pro Max takes a clear lead. It finishes with 93% remaining, followed by the Pro at 87% and the Duo at 84%.
iPhone 18 Pro Max
93%
Battery remaining
iPhone 18 Pro
87%
Battery remaining
iPhone Duo
84%
Battery remaining
The Duo is now 9 percentage points behind Pro Max and 3 points behind Pro. Pro Max also finishes ahead of Pro in both tasks, making it the more consistent performer across these two tests.
If your typical evening is several episodes on the sofa, the playback result is the one to pay attention to. You get more battery left on Pro Max, while the Duo trades some of that reserve for its folding-screen experience.
Why does the Duo’s battery ranking change so much?
Mediastorm’s explanation centers on screen utilization: how much of the inner display is actively showing an image. The camera interface and the video player use that space differently.
Camera recording leaves more of the screen black
The recording preview occupies only part of the Duo’s inner screen. Those large black areas help reduce the display’s contribution to power use during the filming session.
Watching video changes the display workload
When more of the panel is used for moving images, the screen demands more power. The Duo’s last-place finish in the three-hour playback test shows why its strong recording result does not carry over to every video task.
This is why a larger screen does not translate into the same battery penalty in every app. What is on that screen matters too. For a closer look at how widescreen content fits the foldable panel, see our iPhone Duo vs Pro Max 16:9 video-size comparison.
Which iPhone should you choose for battery life?
iPhone 18 Pro Max: the strongest choice for watching video
Pro Max leads the three-hour playback test at 93% remaining and stays close to Duo during recording at 59%. If long viewing sessions are a priority, it is the clearest pick from these results.
iPhone Duo: a surprisingly capable filming companion
Duo leads the two-hour recording test at 61%. Its folding display adds a different way to frame and review footage, but the 84% playback result is the trade-off to remember if you spend hours watching video.
iPhone 18 Pro: choose it for the smaller format
Pro finishes between the other two during playback at 87%, but falls furthest behind during recording at 45%. The camera-heavy test makes the battery difference from Pro Max especially noticeable.
My takeaway: Pro Max is the more balanced battery pick across these two tasks, while Duo is much stronger at filming than you might expect. If you want the foldable, the recording result is a good reason to feel less anxious about using its camera for longer sessions. If watching video is your main use, Pro Max keeps the bigger reserve.
How quickly can the Duo recharge after a long session?
In the same review, the Duo took 88 minutes to charge from 0% to 100% over a cable, reaching a measured peak of 36–37W. Pro Max completed its full charge in 70 minutes.
That is an 18-minute difference for a full refill. For an outing built around filming, a charging break is still useful even though the Duo’s two-hour recording result is strong.
FAQ
Is the iPhone Duo better than Pro Max for video battery life?
For the two-hour recording task, Duo finished slightly ahead: 61% remaining versus 59%. For three-hour video playback, Pro Max finished well ahead: 93% versus 84%.
Are 93%, 84% and 87% the battery levels before the recording test?
Those are the results after three hours of 16:9 video playback: Pro Max 93%, Duo 84% and Pro 87%. The two-hour recording results are a separate comparison.
Does opening the Duo always mean much higher battery drain?
The review shows that what fills the screen matters. During recording, large black areas surround the preview; when more of the display is showing moving content, its power use increases.
Which phone had the least battery left after recording?
iPhone 18 Pro finished the two-hour recording test at 45%, compared with 59% on Pro Max and 61% on Duo.
Watch the original battery test
Video source: Mediastorm (影视飓风) — 折1万次，会坏吗？iPhone Duo深度评测. Battery results and the screen-utilization explanation above are drawn from the review’s battery-life segment. The three comparison images are credited to the same video.
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