Flagship smartphones are entering a new era, with several models now equipped with batteries of 7,000mAh or more. Within just a month, four such devices arrived on our test bench: the OPPO Find X9 Pro, Realme GT 8 Pro, iQOO 15, and OnePlus 15. Despite offering similar battery capacities, real-world endurance ultimately depends on how well each phone is optimised. Their respective reviews saw how the smartphone’s battery fared individually.
In this article, we’ll be taking a look at which smartphone delivers the longest battery life. To determine that, all four were subjected to the same set of tasks and tested in identical conditions to measure how quickly their batteries drained.
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Why are brands using bigger batteries?
It is the advancement in battery technology. All of these brands have moved away from traditional lithium-ion batteries to silicon-carbon batteries, which can hold more charge without being bulky. The OPPO Find X9 Pro, which packs the highest battery capacity at 7,500mAh, measures just 8.3mm in thickness and weighs 224 grams. To put it in perspective, the iPhone 17 Pro Max, which boasts a 4,832mAh battery, is both heavier and thicker than the OPPO smartphone. There are other components involved as well, but the battery adds significant weight to the smartphone.
| Smartphone | Battery | Thickness & weight |
| OPPO Find X9 Pro | 7,500mAh | 8.3mm & 224 grams |
| OnePlus 15 | 7,300mAh | 8.2mm & 215 grams |
| Realme GT 8 Pro | 7,000mAh | 8.2mm & 214 grams |
| iQOO 15 | 7,000mAh | 8.17mm & 216 grams |
The main concern with silicon–carbon batteries is long-term durability, and only real-world use over the years will reveal how they truly age. Until then, we can only go with the brands’ claim that the batteries should retain around 80 per cent of their capacity even after years of regular use.
With that being said, let’s take a look at how these batteries perform in their respective tests.
PCMark battery test
This is a synthetic battery test that puts each phone through a mix of tasks, browsing, scrolling, editing and more, until the battery falls below 20 percent. All handsets started at a full 100 percent charge, with volume set to 50 percent, screen brightness fixed at 80 percent, and a similar environment for consistency.
The OnePlus 15, equipped with a 7,300mAh battery, topped the chart with a runtime of 17 hours and 6 minutes. Close behind was the OPPO Find X9 Pro at 16 hours and 1 minute, an unexpected result considering it carries the largest battery of the group at 7,500mAh.
In the third and fourth place, we have iQOO 15 and Realme GT 8 Pro with their respective runtimes of 13 hours 7 minutes and 12 hours 45 minutes, respectively. Both smartphones come with a relatively modest 7,000mAh battery.
YouTube video streaming
This test analyses the smartphone’s endurance while streaming videos, which has become a key aspect in today’s day and age. All four phones were connected to the same Wi-Fi network to stream a 30-minute HDR video on YouTube with 50 percent screen brightness and volume levels.
Once again, the OnePlus 15 appears to be the better optimised device, dropping only 2 percent during this stage. The OPPO Find X9 Pro, Realme GT 8 Pro, and iQOO 15 each saw a 3 percent decline. The gap may look small in a short test, but if you regularly stream or watch a lot of multimedia content, you know where to look.
Gaming
The iQOO 15, Realme GT 8 Pro, and OPPO Find X9 Pro may not market themselves as gaming phones like the OnePlus 15, but they’re all more than capable of handling demanding titles with ease. Each handset is powered by a top-tier chipset and backed by an efficient cooling system, helping minimise throttling and maintain stable frame rates over extended sessions. But what about their battery endurance?
To test that, we downloaded BGMI, Call of Duty: Mobile, and Real Racing 3 on all four smartphones and played them for 30 minutes each with identical graphics, frame rate, brightness, and volume settings. The OPPO Find X9 Pro turned out to be the most efficient, consuming an average of 4 percent battery.
The Realme GT 8 Pro followed with an average battery drop of 4.6 percent, while the iQOO 15 came in at 5 percent. The OnePlus 15 turns out to be less favourable, with an aggregate of 16 percent battery loss after playing all three games, an average drop of 5.3 percent. This may not be huge, but something to keep if you game for an extended duration.
Real-world usage
Alongside our standard lab tests, each phone was also used as a daily driver by our in-house reviewers to gauge its real-world battery performance.
OnePlus 15
“By the end of the day, I was left with around 40–50 percent battery life.” – Sanket Vijayasarathy
That was our Senior Reviewer Sanket Vijayasarthy’s impression after reviewing the OnePlus 15. He further added that even on punishing days, including benchmarking, an hour of streaming, and long gaming sessions in Call of Duty Mobile and BGMI, it still wrapped up the day with considerable juice left in the tank.
That’s enough to get halfway through the next morning without charging. Its combination of efficiency and a larger battery makes it the best of the bunch for anyone who wants genuine two-day potential.
iQOO 15
“I was comfortably getting a day’s battery, and then some, between charges.” – Ashish Kumar
I reviewed the iQOO 15 and concluded that the battery is reliable. Even with a routine that mixes video streaming, map navigation, social media scrolling, casual browsing, and a couple of BGMI sessions, the phone consistently lasts a full day. This makes the iQOO 15 a safe choice for commuters and anyone who doesn’t want to hunt for a charger before bedtime.
Realme GT 8 Pro
“The battery life was my biggest complaint.” – Dhruv Joshi
My colleague Dhruv Joshi noted in his Realme GT 8 Pro review that the device’s battery struggles in real-world use. With 5G active throughout the day and about two hours of heavy camera use, the phone often dipped to around 10–12 percent by 9 PM. Screen-on time wasn’t impressive either, averaging roughly six hours per day. For power users, or anyone who spends a lot of time on mobile data and the camera, the endurance may feel underwhelming.
But, for regular users, that battery backup should prove sufficient.
OPPO Find X9 Pro
“It comfortably powers through an entire day without issue.” – Ashish Kumar
While reviewing the OPPO Find X9 Pro, it was observed that light users can stretch the handset’s battery to two days. Heavier days still see it comfortably lasting from morning to night, with constant map navigation, photography, social media, and messaging. The handset delivered about six and a half hours of screen time, making it a dependable option for travellers and content creators who need consistent all-day backup.
Fast charging showdown
No matter how impressive the battery life is, nobody wants to spend ages tethered to a wall socket. And bigger batteries inevitably take longer to recharge, but all four phones tackle that problem with high-speed charging. Moreover, each one includes a compatible fast charger right in the box.
| Smartphone | Battery Capacity | Charging Support | Charging time (20% to 100% ) |
| OnePlus 15 | 7300 mAh | 120W Super VOOC Charging | 30m |
| OPPO Find X9 Pro | 7500 mAh | 80W Super VOOC Charging | 1h 12m |
| iQOO 15 | 7000 mAh | 100W Flash Charging | 45m |
| realme GT 8 Pro | 7000 mAh | 120W Super VOOC Charging v3.0 | 39m |
Surprisingly, the OPPO Find X9 Pro with the biggest battery offers the slowest charging speeds at 80W SuperVOOC, and eventually takes the longest to charge. During our lab test, the handset achieved a full charge from 20 percent in 73 minutes.
The iQOO 15 and Realme GT 8 Pro, meanwhile, took 39 and 45 minutes, respectively, for the same charge cycle. The extra six minutes for the iQOO is understandable, given its slower 100W charging solution as opposed to 120W on its counterpart.
The OnePlus 15 hits a sweet spot of 120W for its 7,300mAh battery. 30 minutes is all you need to recharge the OnePlus smartphone from 20 to 100 percent, making it a sound choice for people who are always on the go and don’t want to linger by a wall adaptor.
Verdict
| Summary | Winner | Price |
| Best overall battery performer | OnePlus 15 | Rs 72,999 |
| Balanced efficiency | OPPO Find X9 Pro | Rs 1,09,999 |
| Reliable for everyday use | iQOO 15 | Rs 72,999 |
| Adequate backup | Realme GT 8 Pro | Rs 72,999 |
That was our flagship battery showdown, featuring high-end 2025 phones with batteries of 7,000mAh or more. Despite a near-identical setup, you can see how different the smartphones have been optimised for real-world efficiency.
The OnePlus 15 is the overall winner. The handset leads in PCMark tests, sips power during video playback, and consistently ends demanding days with nearly half its battery remaining. The OPPO Find X9 Pro follows closely, offering strong all-day reliability and the best gaming efficiency, though its charging speed is the slowest of the group.
The iQOO 15 synthetic endurance may not match its battery size, but it delivers dependable full-day stamina with mixed use. The Realme GT 8 Pro, meanwhile, lags behind in both benchmarks and real-world longevity, especially on 5G and heavy camera days, though average users may still find it adequate.
While the OnePlus 15, iQOO 15, and Realme GT 8 Pro are all priced the same at Rs 72,999 for their base variants, the OPPO Find X9 Pro will set you back to a whopping Rs 1,09,999.
OPPO Find X9 Pro Images
