When your phone's battery gets really low, like down to 2%, what do you do? My guess is that you plug it in to charge or reach for a battery bank. If you can't recharge, you turn on your phone's low-power mode to eke out every last drop of power you have left. Well, that's not what CNET's David Lumb did when his phone was at 2%. He started playing the game Dead Cells on it.
No, Lumb isn't a masochist; he's a phone reviewer. After 45 minutes of gameplay, his phone finally dropped to 1%, at which point it automatically shut down. Lumb was reviewing the new OnePlus 15, which has a special silicon-carbon battery. At 7,300 mAh, it's one of the largest capacity batteries of any phone that CNET has ever tested. For perspective, the iPhone 17 Pro Max has a 5,088-mAh battery and scored top in our CNET Labs battery tests in September.
Battery life is arguably the most important feature in any mobile device. In a CNET/YouGov survey, readers ranked "longer battery life" second only to price among reasons to upgrade to a new phone. The more we use our phones, the more we thirst for more hours away from the charger, and phone-makers are responding with longer-lasting batteries.
The OnePlus 15's 7,300-mAh battery is enormous, but there are a handful of other phones that CNET has tested with a 7,000-mAh capacity battery or higher: Gaming phones such as the 2024 RedMagic 10 Pro and its follow-up, the RedMagic 11 Pro have 7,050-mAh and 7,500-mAh batteries, respectively. The Oppo Find X9 Pro has a behemoth 7,500-mAh battery but it isn't sold in the US. I should note that OnePlus is a subsidiary of Oppo.
The secret sauce giving these phones such extraordinary capacity is that they have silicon-carbon batteries, a relatively new type of power source that can increase capacity without requiring a larger physical battery. That's especially important in a phone, where battery size is severely limited.
"Silicon possesses a much higher energy storage capacity than graphite. Our innovation lies in integrating this material at an industry-high 15% content, which fundamentally enables greater energy density," Rudolf Xu, OnePlus senior product marketing manager, told CNET. "Paired with the customized dual-cell design, it allows us to pack a massive 7,300-mAh capacity."
OnePlus is one of a handful of phone-makers taking advantage of silicon batteries. And it's only a matter of time before other device manufacturers follow.
Silicon-carbon vs. graphite batteries
The OnePlus 15's 7,300-mAh battery can be recharged from empty to full in 45 minutes. Andrew Lanxon/CNET
Before you can really appreciate what OnePlus has done, it's worth explaining some terminology. Battery capacity, measured in milliampere-hours (mAh), is just one factor that determines how long your phone lasts before you have to recharge it.
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