When it comes to smartphones, we’re basically living in two different worlds right now. On one side, you have brands like Samsung and Apple still sticking with lithium-ion batteries, while on the other, companies like Oppo, and Xiaomi have moved to silicon-carbon battery tech.
This change means that silicon-carbon batteries on these newer flagships are often around 25-35% larger than what traditional lithium-ion phones offer. Yet, brands like Apple and Samsung still claim “all-day battery life” in their presentations.
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Hardware and specs
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Before we get into the test results, let’s quickly go through the hardware and internal specs of these phones. While Apple doesn’t officially publish battery capacities of the iPhones, credible reports suggest the iPhone 17 Pro Max packs an estimated 4,823mAh battery on models with a SIM tray, while the U.S. eSIM-only version is said to feature a larger 5,088mAh cell.
This is a noticeable jump over previous models. Alongside the bigger battery, Apple has also upgraded the cooling system on the iPhone 17 Pro Max, adding vapor cooling for the first time to manage heat from the A19 Pro chipset. It also supports faster wired charging, going up to 40W with the right charger.
(Image credit: Sanuj Bhatia / Tom’s Guide)
The Oppo Find X9 Ultra, on the other hand, packs a massive 7,050mAh silicon-carbon battery. This is easily one of the biggest you’ll find on an ‘Ultra’ flagship. It also leads in charging speeds, with support for up to 100W wired charging.
On top of this, similar to most flagship phones in 2026, the Find X9 Ultra is powered by the Snapdragon 8 Elite Gen 5 chipset, and Oppo has included its 3D Cryo-velocity cooling system to keep temperatures in check during heavy use and maintain sustained performance.
Overall, the Oppo Find X9 Ultra clearly holds the lead on paper and is already shaping up to be one of the top contenders for the best battery life phones, but does that actually translate to real-world usage? Here’s what we found.
Battery life & YouTube test
(Image credit: Sanuj Bhatia / Tom’s Guide)
To run the battery test, we put both the Oppo Find X9 Ultra and the iPhone 17 Pro Max through a YouTube playback test to see how they hold up. We played the same YouTube video at 1080p resolution over Wi-Fi on both phones, kept brightness levels similar (around 50%), and ran the test for three hours starting from 100%.
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After the three-hour mark, the iPhone 17 Pro Max dropped to 90%, which is honestly very impressive on its own. However, the Oppo Find X9 Ultra managed to go a step further, ending the test at 94% after the same three hours of playback.
Swipe to scroll horizontally3 hours of YouTube from 100% charge
Phone
Battery percentage
iPhone 17 Pro Max
90%
Oppo Find X9 Ultra
94%
This shows that while Apple has made solid improvements with the iPhone 17 Pro Max, the Oppo Find X9 Ultra clearly comes out ahead when it comes to battery life in this test.
The gap may not look massive on paper, but losing just 6% over three hours of continuous video playback is something you don’t see often, and — extrapolated out — it gives you a lot of confidence the Find X9 Ultra can comfortably last a full day, no matter how you use it.
Charging test
(Image credit: Sanuj Bhatia / Tom’s Guide)
No matter how big the battery is, you’ll have to charge your phone sooner or later, so we also tested the charging speeds.
For this, we used Apple’s 40W charger (with a 60W peak output) for the iPhone 17 Pro Max, while the Oppo Find X9 Ultra was charged using a OnePlus 100W SuperVOOC charger. Since OnePlus and Oppo share the same charging tech, and the Find X9 Ultra supports the same 100W speeds, this setup shouldn’t skew the results.
Swipe to scroll horizontallyCharging test from 0%
Phone
15 mins
30 mins
iPhone 17 Pro Max
35%
64%
Oppo Find X9 Ultra
44%
74%
Apple claims the iPhone 17 Pro Max can hit 50% in around 20 minutes. In our testing, it reached 35% in 15 minutes and 64% in 30 minutes, which is still pretty solid.
But once again, the Oppo Find X9 Ultra pulls ahead. It reached 44% in 15 minutes and 74% in 30 minutes, and that’s while charging a much larger battery, which makes the result even more impressive.
Bottom line
(Image credit: Sanuj Bhatia / Tom’s Guide)
Overall, this test once again shows that while Apple has clearly improved the battery life and charging speeds on the iPhone 17 Pro Max, competitors in the Eastern markets are pushing things even further.
Speaking for myself, the Find X9 Ultra is easily one of the best phones I’ve used in a while, not just for battery life, but also for its camera performance and overall design.
It really makes me wonder how much better Apple and Samsung devices could get once they finally adopt silicon-carbon battery tech. But until that happens, it doesn’t feel like they’re quite catching up to what brands like Oppo are doing right now.
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