Battery life is rated at up to 5 days of use between charges, which I confirmed in my testing. As with most fitness trackers, this one comes with a proprietary charging cable (it clamps onto the watch), not a standard Micro-USB cable. So lose it and you'll have to buy another one.
This is the first product in the Garmin Vivo family to estimate VO2 max, a measurable indication of aerobic performance that was previously available only in higher-end Garmin running watches. Your VO2 max score translates into a fitness level, ranging from poor to superior, and it's also used to calculate your fitness age, "a relatable metric that puts a user's fitness level in terms of an age."
The idea, of course, is to increase your VO2 max and reduce your fitness age through a steady workout regime.
Overall, I liked the Vivosmart 3, particularly its light, slim design, and thought both the touchscreen and the device were pretty responsive. I found it a little more comfortable to wear than the Fitbit Charge 2 and liked that I didn't have to worry about jumping into the pool or another body of water with the device on. That said, I accidentally fully submersed the Fitbit Charge 2 a few times and it survived even though it's only rated as being splashproof.
Comparatively though, I thought the Fitbit Charge 2 was a little more responsive, more user friendly and the display is a little easier to read. Both are good, but I also found it annoying that the Vivosmart 3's display didn't always turn on when I turned my wrist.
My gut says that although the Vivosmart 3 has enough high-end features to satisfy serious athletes, it won't necessarily appeal to them because they'll want something with a bigger face that's easier-to-read and operate. Conversely, more casual athletes may only stick to the top-line features because scrolling through the menus to access the rep counter, for example, requires a little digging.
Ultimately, the Vivosmart 3 is a very good activity tracker that's waterproof and feature-packed. But as you can probably tell by now my only reservation about it is that it's a little hard to navigate and access all those features quickly and easily -- and to make use of them in general.