I've been testing the $330 OnePlus Watch 3 for 48 hours and have found it to be, so far, a powerhouse smartwatch wrapped in a sleek, understated design. OnePlus aims to compete with its Android rivals by offering a robust set of health and fitness features, and the promise to blow them all away with a five-day battery life under normal use.Having heard similar promises about smartwatch batteries before, I was skeptical. Companies often hype up battery life, only to bury in the fine print that it requires power-saving mode -- stripping away "smart" features and turning the watch into nothing more than a glorified digital clock. I was pleasantly surprised that the default settings on the Watch 3 include full use of all its features, minus the always-on display, which I would normally activate.The only change I made was swapping the analogue-style watch face for one that displayed battery life at a glance, along with workout shortcuts, weather and fitness tracking. Big mistake. Turns out, I had unknowingly picked one of the worst offenders -- a level three out of three on the Wear OS battery drain scale.During my first two days with the Watch 3, I used it to receive text and email notifications, track an hour-long outdoor run with GPS, log an indoor strength workout andtrack two nights of sleep. As a result, the Watch 3's battery dropped to 50% within the first 48 hours.While it doesn't quite hit the promised five days, I should still get four full days of battery life from the Watch 3 on a single charge -- impressive, considering mostAndroid smartwatchesstruggle to last three. For my full review, I'll switch to a lower-power watch face to see if I can push it to OnePlus' five-day claim.There's a lot more to unpack with the Watch 3, and so far, I'm pleasantly surprised.Battery life takes center stage The Watch 3's best feature, after two days of testing, is its battery life. Vanessa Hand Orellana/CNETOnePlus' claim to fame initially was delivering quality devices at more affordable prices than high-end competitors like Samsung and Google. And the Watch 3, the fourth from the Chinese company, aims to shake up some of that tradition.Unlike the original $160 OnePlus Watch and last year's $180 Watch 2R, whose low prices were the main appeal, the Watch 3 prioritizes its more premium appeal over a low price. OnePlus wants the Watch 3 to be a premium flagship device, putting it in direct competition with other Watch OS devices like the Google Pixel Watch 3 and Samsung Galaxy Watch 7. What could set it apart, if it delivers, is its battery life.OnePlus claims the Watch 3 can last five days on its default settings. That's thanks to a large 631mAh battery and a dual-chipset system that uses its Snapdragon W5 processor to focus on powering app usage, while its BES2800 MCU Efficiency chip handles low-powered background tasks.In my first two days, I was impressed with the Watch 3's battery life, despite my choice of using a battery thirsty watch face. It's worth noting that the Watch 3 has an ultra power-saving mode, which OnePlus claims can last up to 16 days on a full charge.Design upgrades and interface This is what the OnePlus Watch 3 looks like right out of the box. Vanessa Hand Orellana/CNETThe OnePlus Watch 3 keeps the sleek stainless steel design of its predecessor, with some notable upgrades. It has a rotating crown with an easy-to-grip texture and a titanium bezel surrounding the screen -- reminiscent of the rotating bezels on the early Samsung watches that I loved. This one is thinner and stays in place, but I like how it elevates the design, making it look less like a giant circular 1.5-inch AMOLED display strapped to my wrist. The screen is bright and easy to see even in direct sunlight. The watch comes in silver or black, with rubber straps that are comfortable to wear all day and night.The Watch 3 runs on Wear OS 5, with additional OnePlus design and features, like the OHealth app that you'll need to download on your phone to access the watch's full range of health tracking features.The interface of Watch 3 feels a bit sluggish, with a slight lag in response time. It's hard to tell whether this is a Wear OS issue or if it's the actual watch but navigation isn't entirely seamless -- though it did improve as I got more familiar with the buttons and gestures.The interface isn't particularly intuitive either -- some settings, like workout views, require digging through menus (a known Wear OS issue). I also had trouble setting up my account in the OHealth app and syncing it with my Google health data. This may be due to using a developer version of the app, but it's cumbersome nonetheless.Accessing all my health data through the OHealth app hasn't been too bad, thanks to its visual, user-friendly interface.Health and fitness features Here's the OnePlus Watch 3 next to a OnePlus 13 with the OHealth app open. Vanessa Hand Orellana/CNETOnePlus' investment in health and wellness is evident in this watch. In addition to basics like heart rate and calories, it measures more nuanced health metrics, like cardiovascular health, SPO2, wrist temperature and general well-being (which includes emotional and stress levels), though not without some caveats. None of these features are FDA-approved, meaning they aren't meant to be used as medical-grade data. Additionally, the ECG feature isn't available in the US or Canada. The Watch 3 also lacks menstrual health tracking -- an oversight, in my opinion -- especially since wrist temperature monitoring, now standard on its main rivals, could be extremely useful for ovulation tracking.The Watch 3 also debuts a 60-second health check-in, a feature that checks all your vitals in one spot by pressing your finger on the watch's bottom button. My first health check-in was concerning and displayed a red exclamation mark with the word "abnormal" next to it. Upon further inspection, it turns out all my vitals were in range, but it was my sleep score that was skewing the results. I'll admit, my sleep habits aren't great, partly due to my one-year-old daughter, but I'd argue that I at least deserve a passing grade.In terms of fitness, the OnePlus Watch 3 covers all the basics, with more than 100 different sports modes, six of which it detects automatically: running, walking, rowing, elliptical machine, cycling and swimming. It also offers a "professional" mode for 11 sports that keeps tabs of more nuanced metrics related to that sport. For runners, it tracks form and foot balance, while for tennis players, it measures swing speed and stroke. While it may be overkill for most, as a runner who recently learned how to leverage heart rate zones to intensify workouts, I'm excited to nerd out on these additional metrics.Another key feature for outdoor sports enthusiasts is its dual-frequency GPS tracking system, which OnePlus claims can position you accurately even in challenging environments, such as crowded cities surrounded by high rises. I live in an entirely different environment, more sheep than skyscrapers, so I haven't been able to fully test this claim. It did position me perfectly on my usual trail run through oak trees and vineyards.With an IP69 rating, the OnePlus Watch 3 is also water-resistant up to 50 meters.Everything ElseI plan to dive deeper over the next few days and test some of the Watch 3's other features for my full review. But for now, if battery life is at the top of your wishlist for a smartwatch, as it is mine, this is one Android smartwatch that's definitely worth considering.The OnePlus Watch 3 is now available for presale through OnePlus's website, with an official release date set for February 25.