While fans may quibble over the various drawbacks to this year’s OnePlus 15, one of the phone’s biggest claims to fame is its humongous 7,300mAh silicon-carbon-based (Si-C) battery. Its sibling phone, the OPPO Find X9 Pro, boasts an even larger 7,500mAh cell, making them two of the largest battery capacities available on global markets.
For comparison, the Apple iPhone 17 Pro Max features a 5,080mAh cell, the Google Pixel 10 Pro XL offers 5,200mAh, and the Samsung Galaxy S25 Ultra boasts around 5,000mAh. Those were considered very robust capacities just a few months ago, despite being slightly smaller than the first-wave of 6,000mAh Si-C batteries. However, they are now eclipsed by nearly 50% compared to the second wave of Si-C-equipped smartphones.
It goes without saying that a 50% larger battery makes a significant difference to screen-on time. We’ve been pleased to see the OnePlus 15 take us through two full days and even squeeze into a third, and I’m having an even harder time running down the Find X9 Pro except under heavy gaming. Anecdotally, both phones comfortably last through the second day with some battery left, where previous flagships would typically run out before the end of the second day, if not the first.
To put some real numbers on those differences, we ran both phones through our suite of battery-life benchmarks (web browsing, camera use, etc.). Let’s start by examining the first generation of silicon-carbon batteries from OnePlus and OPPO versus these latest Si-C models.
The results are what you’d expect — mostly. The OnePlus 15 and OPPO Find X9 Pro offer notable improvements over their predecessors across a range of real-world use cases. The exception appears to be the OnePlus 15’s camera and web test results, which are somehow slightly worse, possibly due to the change in hardware and/or task scheduling.
Taking an average across our real-world battery tests, the OnePlus 15 achieves an additional 19% battery life compared to the OnePlus 13, which closely aligns with its 21% larger battery capacity. The OPPO Find X9 Pro is slightly better, winning by an average of 37% across our tests from a 27% increase in cell size. This difference likely stems from their chipsets (Snapdragon 8 Elite Gen 5 versus MediaTek Dimensity 9500, respectively) and software-level battery management optimizations.
Compared to flagships with traditional Li-ion batteries, these gains hold up well too. The OnePlus 15 averages 40% longer battery life across our tests compared to the Google Pixel 10 Pro XL (matching the 40% larger cell). However, it only scores 28% better than the Galaxy S25 Ultra, despite having a 46% larger cell. The Find 9 Pro is slightly more consistent, averaging 57% better than the Pixel 10 Pro XL (for a 44% larger cell) and 52% better than the S25 Ultra (for a 50% larger battery). That’s enough to comfortably reach the end of that second day rather than one and a half.
Based on our real-world tests, expect 30% to 50% longer battery life over mainstream flagships.
That said, those averages are not uniform — gains vary depending on workload and device. The OnePlus 15’s improvements aren’t as consistent as those of the OPPO. Still, it’s safe to say the battery gains are real. Even accounting for workloads, potential inefficiencies, and hardware changes, these large silicon-carbon cells deliver close to their theoretical advantage when averaged out over a day or more of real-world use.
Are there any downsides to Si-C batteries?
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