A dead smartwatch is useless—a black screen, staring blankly back after you raise your wrist to check the time for the umpteenth time. Battery life remains the number one problem with these wearables. Apple has made the same 18-hour battery life claim on the Apple Watch since the original, and although it can extend past that these days, you're still not going to get a two- or three-day battery life without limiting some functions severely.

Lo and behold, OnePlus has delivered what the top dogs haven't with its new OnePlus Watch 3: a thumping five-day battery life. While it's slightly bigger than its predecessor, this smartwatch doesn't rely on size alone to stretch run time, but on new battery technology. I have charged it once in the week I've been testing it—at the end of the fifth day—without having to turn off any features.

Yes, fitness trackers and some watches from brands like Garmin can last several weeks, but none of those have access to the wealth of apps and smart functions as an Apple Watch or Wear OS watch. That's what makes this $330 OnePlus smartwatch exciting.

Battery Gains

The impact of a five-day battery life is huge. Too often have I gotten into bed and looked at my watch, only to realize it's going to die in the middle of my slumber, so I begrudgingly trudge to the charger on my desk and leave it there. Too often have I gone a day or two with a dead watch on my wrist because I kept forgetting to put it back on the charger. There has been none of this with the OnePlus Watch 3.

This is possible thanks to the new silicon-carbon battery technology inside the watch—OnePlus first used it in the OnePlus 13 phones, but companies like Honor have been employing it for some time. These batteries are denser, allowing them to carry a higher capacity without requiring a thicker battery. That's why the OnePlus 13 can fit a big 6,000-mAh cell despite being thinner than the OnePlus 12, which has a 5,400-mAh cell. OnePlus calls this its Silicon NanoStack Battery, and so the OnePlus Watch 3 has a 631-mAh battery compared to its predecessor's 500-mAh cell.

That's not all, OnePlus continues the dual-engine architecture that it debuted last year. The OnePlus Watch 3 has two operating systems and two chipsets. The Qualcomm Snapdragon W5 chip powers Google's Wear OS 5, which handles all the graphics-intensive tasks, whereas an upgraded BES2800 chip runs the Real-Time Operating System, which manages many of the background tasks.

Splitting this workload, in conjunction with the beefier battery, nets you five days of juice. Mind you, this is with the default mode. If you turn on power-saving mode, OnePlus claims 16 days of battery life. For context, Apple claims its Low Power Mode can make the Apple Watch Series 10 last 72 hours.

Almost like clockwork, I lost roughly 25 percent power per day until I was left with 10 percent by 8 pm on the fifth day. That includes roughly one auto-tracked activity per day. The caveat? This five-day battery life isn't possible if you turn on features such as continuous heart-rate monitoring, SpO₂ tracking, and the “assess breathing problems” function during sleep. The always-on display was also turned off. None are enabled by default, but if you toggle them on, you can probably cut a day or two from the longevity, though I haven't tried it with the full gamut to say for sure.

When the watch finally did need to be charged, I popped it on the magnetic proprietary charger and it juiced back up quickly. I love that the charging cradle has a USB-C port, so you can just bring the tiny dock around and use the same cable you'd use to charge your phones or laptop.

Fast and Smooth

The Watch 3 has a slightly sportier look this go around. It's a smidge bigger with a 1.5-inch AMOLED display, but I find it quite comfortable to wear—even to bed. OnePlus says it has improved the strap design to sit closer to the wrist for comfort and better accuracy with the sensors. The size may inevitably be too large for some folks, so I'd love to see OnePlus introduce a smaller option in the future à la Google's Pixel Watch. It'd cut the battery life, but I'm sure smaller wrists would still appreciate two or three days on a single charge.

There's one programmable button on the bottom right edge, and above it is the digital crown, which also doubles as a configurable button. Last year, you couldn't scroll the interface by rotating the crown, but that's now remedied, and there's some nice haptic feedback as you scroll through. I truly don't have any qualms about the hardware—it's IP68-rated and can handle being submersed to about 50 meters (in freshwater). A sapphire crystal protects the bright screen with a new titanium bezel, along with the same stainless steel case. The 22-millimeter strap is easy to swap.

Performance is buttery smooth, which needs emphasizing, because it wasn't too long ago when basic operations on a Wear OS smartwatch were met with stutters and lag. And all the usual functions work well. I've taken calls on the watch, checked notifications, scrolled through my upcoming calendar events, responded to Slack messages, and followed along with navigation while walking.

Health Focus

The biggest improvements, however, are in health and fitness. One of my complaints in my OnePlus Watch 2 review was that the device was “missing health features,” and there were some accuracy issues. It seems as though OnePlus took that to heart. In comparison with the Pixel Watch 3, my heart-rate data was very similar, though I found the OnePlus took longer to show my data than Google's watch. New features also include an electrocardiogram (ECG), wrist skin temperature sensing, irregular heart-rate notifications, and fall detection.

Unfortunately, bad news for US and Canadian customers: OnePlus says it did not “receive official certification” from the US Food and Drug Administration for the ECG, so that function will not be available in these regions. The company did not explain why the ECG wasn't cleared in the US, but globally it's a different story.

Sleep tracking is more accurate now, even picking up the occasional moments when I fall asleep on the couch. I've noticed richer data analysis in the OnePlus OHealth app. It extrapolated, for example, that my awake time was somewhat long one night, and that could be impacted by my sleep environment.

I didn't get much out of the wrist temperature, though this may help women predict periods as my colleague has found using other smart wearables with skin-temperature sensors. I did give the new Vascular Health app a try—it measures arterial stiffness and subsequent risk of cardiovascular disease. Thankfully, my result was “Normal.” You can also get “Low Risk” and “High Risk.” It's hard to measure the accuracy of this, though I can say for sure that my physician has yet to mention any cardiovascular issues when I visit. Of course, OnePlus is quick to mention that these results are not intended for use in diagnosis or treatment.

One new feature that's not available yet is 60s Health Check-In. The idea is that within 60 seconds, you can tap your finger on the scan button and get results for six metrics: heart rate, blood oxygen (SpO₂), mental wellness, wrist temperature, sleep quality, and vascular age. OnePlus says this will arrive in March.

The only metric I don't care much for is Mind and Body. OnePlus claims this tool uses the heart-rate variability, resting heart rate, and activity intensity data to asses stress levels. More often than not, I found the results vague and not helpful. It keeps saying, “Looking good. You're dealing with stress like a pro”—even though I didn't change my habits and had varying levels of stress over the past week.

While it may still be a step or two behind competitors like Samsung and Google, it feels like OnePlus is quickly catching up in health and fitness. It's also putting its money where its mouth is—the company recently opened up a new Health Lab in China to increase research and development and improve testing methodologies.

Health aside, I keep coming back to the five-day battery life. This is especially useful after a year or two of daily use—by then other smartwatches may struggle to last a full day, but the Watch 3 should still be able to go a few days on a single charge.

It's too bad that OnePlus is only committing to two years of software updates. Samsung and Apple support their smartwatches for longer, and this would pair well with the OnePlus battery longevity story. Still, this is a sacrifice I'm willing to let slide because, guess what? I don't have to charge my damn watch every day.