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?
Mishaal Rahman / Android Authority
Of course, bigger batteries take longer to charge (everything else being equal). The OnePlus 15 is slightly slower to fill than the OnePlus 13 as it boasts the same charging power capabilities. It takes approximately 40 minutes compared to 35 minutes for the OnePlus 13.
The OPPO Find X9 Pro is more conservative, spending very little time at its peak 65W recorded power level and instead charging at a modest 32W or so. As a result, the phone takes over 68 minutes to fill, which is a bit longer than the Galaxy S25 Ultra. That’s not quite as bad as the notoriously slow Pixel 10 Pro XL, but it’s hardly fast.
Thankfully, though, even just half an hour on the charger should be enough to power these huge batteries through a full day of use. That said, we might have to wait a while longer if Si-C batteries are adopted by brands that have typically offered charging speeds much slower than those of OPPO and OnePlus.
Perhaps the biggest unknown with Si-C batteries is how well they age. Traditional Li-ion and Li-Poly cells are often rated for anywhere between 500 and 1,500 cycles or so before falling to 80% of their original capacity, depending on the brand. Google and Samsung are notoriously stuck near the bottom of this range, barely lasting two years of use before reaching their degradation point, while the better brands hold up well over four or five years. Apple, for instance, has increased its count to 1,000 cycles for some of its more premium offerings.
We’ll have to see if these huge batteries hold up as well over many years as they do over several days.
OnePlus states that the OnePlus 15’s battery is rated for 1,400 charge cycles, which is better than the OnePlus 13’s 1,000 cycles for its first-gen SiC cell, but not as good as the OnePlus 12’s 1,600 claim. Still, that’s almost four years if you charged every day. However, the good news is that you shouldn’t need to charge these Si-C phones as often, likely only every other day. It could take twice as long to hit those cycle limits. That said, we don’t yet know how well these Si-C batteries age after this point. With more aggressive electrolyte reactions in Si-C cells compared to Li-ion cells, lithium loss and reduced capacity over time may be more pronounced in these new batteries than in traditional ones.
Still, the battery gains from the OnePlus 15 and OPPO Find X9 Pro are very real. The trade-off is slightly slower charge times, but that’s outweighed by the jump in endurance. We’ll just have to wait and see if these huge 7,500mAh Si-C batteries hold up as well over many years as they do over several days of use.
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