The smartwatch with the best battery life I've tested is also one of the cheapest

If you want all the features of a smartwatch but can’t commit to a big, bulky watch face, you might be interested in a smart band. Xiaomi’s ninth-generation popular fitness band has so many new features that it’s basically on par with any full-fledged smartwatch, just in a smaller, lighter form factor.

The Xiaomi Smart Band 9 features a compact design with a slim watch face and a bright, 1.62-inch AMOLED display that’s packed with almost all the health-tracking features you’d find on any other smartwatch, with fantastic battery life to boot.

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In fact, Xiaomi advertises this device as having up to 21 days of battery life on a single charge, although this number goes down based on how many metrics you monitor at once. That said, the battery life is still pretty fantastic, and even with everything turned on, I was able to get a little over a week of constant monitoring without having to charge it.

So how does the Smart Band 9 differ from a smartwatch? Well, the lines are a little blurred. Basically, it can do all the basic things any smartwatch can do but without the quality-of-life features found on higher-end smartwatches and without deeper, more personalized data insights. Xiaomi does have a line of smartwatches, after all, and naturally, there is some delineation between the feature sets.

The Smart Band 9 has the basics covered, though. It’s accurate at tracking most physical activities and comes with over 150+ sports modes, heart rate and blood oxygen tracking, stress tracking, and, of course, sleep tracking. Additionally, it pairs with your phone to support the most useful connectivity features, such as notifications for emails, texts, calls, etc. It does not have GPS, however, nor does it feature a mic or a speaker. 

The device also requires some manual tuning that other, more premium devices would probably recognize automatically. By default, many of the continuous monitoring features are switched off, and to get the most out of the device, you’ll need to manually turn on the features you want. 

The band coordinates with the Mi Fitness app for Android or iOS for the complete experience. The app is straightforward enough to cover the basics but isn’t overly comprehensive. All the previously mentioned tracking metrics are accessible in the app, which is clean and easy to navigate.

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The Smart Band 9 uses the Mi Fitness three-band rainbow design as its core daily tracking system. It shows your calories burned, steps taken, and daily movement. As you do all three of those things, the bands fill, marking your progress. This concept is used by all manner of wearables, but this one features one of the cleaner designs I’ve seen.

In fact, Mi Fitness is one of the more accessible apps for folks who aren’t well-versed in fitness tracking lingo or are new to the game. It does a good job of spacing out the data so as not to bombard you with numbers and metrics. For that reason, this would also make a great tracker for kids or teens.

Xiaomi says that the Smart Band 9 features a tracking sensor that is 16% more accurate than the previous version. Still, its accuracy sometimes strayed for me, particularly with the more complex metrics. For example, it doesn’t seem to catch when I wake up at night, even if I get out of bed.

Nevertheless, the sleep tracking is about on par with other smartwatches, providing a breakdown of how long you were in each sleep stage, as well as your average heart rate, blood oxygen level, and breathing rate (as long as you turn those features on). Its lightweight and thin form factor also makes it very easy to sleep with, so if wearing a chunky watch to bed feels weird to you, this might be a good option.

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The Smart Band 9 doesn’t have some of the deeper insights that more comprehensive sleep trackers like the Oura ring have, but it will interpret the basics for you and add the data to your overall Vitality Score. This number is the Mi Fitness’ holistic health assessment metric that looks at the last seven days’ worth of data to provide an overarching score based on your age, weight, and activity level.

Xiaomi makes some wearable accessories that connect with its smartwatches and smart bands to provide more accurate data. For example, the Running Clip for the Smart Band 9 is only $12 and clips to your shoe for deeper, more accurate tracking. You just switch the band into running mode to access run cadence, stride length, landing time, landing mode, and more.

Let’s break down some of the things I don’t love about the Smart Band 9. First, the fit is not exactly perfect. Because the device is so small, it tends to lose its optimal position on the wrist. There were multiple instances where I looked down, only to see the sensor light flashing on the bottom of the device, indicating it doesn’t have skin contact.

If you’re a lean person or have smaller wrists, the Smart Band 9 might have a little more trouble positioning itself and lose contact from time to time, especially if you’re moving around. The way around that is to just wear it very tight to your wrist, which may or may not work for you.

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Also, the screen is small. Navigating the menus is functional, but if you have big hands or trouble seeing the tiny 1.62-inch display, the Smart Band 9 might be a little too compact.

When I tested it out during a HIIT workout, the transition from moving around to the little display took some getting used to. Similarly, if you’re mid-run, it’s very difficult to navigate. This is a device you set up before running around.

ZDNET’s buying advice

The Xiaomi Smart Band 9 is a great entry-level device that can do almost anything a smartwatch can do, just in a more basic form. If you’re looking for accurate, actionable insights across specific metrics, you’ll want to invest in a premium smartwatch. Still, the Smart Band 9 and the accompanying Mi Fitness app are well-designed and accessible, great for kids, teens, and folks just starting their fitness journeys. 

The device itself is small and thin, and because of that, might not fit well on certain people, and the display, while very bright, is about half the size of a smartwatch. Its small size makes it very easy to wear to bed for sleep tracking, and it provides the basic roundup of sleep tracking metrics.

If you’re looking for a wearable that can do most of the same things but has a proper watch face, check out the Amazfit Bip 5, which is only about $15 more expensive.