Day 21. Screen still on. 13% left in the tank.
Xiaomi puts a 21-day battery claim on the box for the Watch S5. Numbers on packaging are cheap, so I strapped it on and didn't take it off until the battery ran out. This is what remained.
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Xiaomi Watch S5
The Watch S5 is Xiaomi's shot at the segment above where the S-series has usually parked itself - a 46mm smartwatch built around a leather strap, a proprietary OS instead of Wear OS, and a battery claim it's willing to put a number on: 21 days. On paper it reads like a fitness tracker dressed up for a meeting. On the wrist, over three weeks of actually living with it, it mostly backs that up.
This review covers what that 21-day claim looked like under real daily use, how the case and strap actually wear, and what the sensor and software stack are like day to day - sport tracking, sleep, stress, SpO2, watch faces and the app pairing experience included.
A 46mm case that talks itself out of feeling like one
46mm is a number that usually makes me wince a little - that's dress-watch-that-forgot-its-diet territory on most brands. The S5 doesn't wear like it. It's slim off the wrist rather than domed, the case tapers instead of just stopping, and the whole thing sits lighter than the spec sheet has any right to suggest. No dead-arm feeling by hour three, no catching on cuffs.
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Credit goes partly to the leather strap. It's the detail that pulls the whole watch upmarket - swap in the usual silicone loop and this reads like any other fitness tracker; with leather it reads like something you'd choose to wear even with the screen off. Slim, premium, and it doesn't announce itself, which is exactly the register I wanted from a watch I'd be wearing to sleep for three straight weeks.
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The bezels are doing a lot of the work here too. The 1.48" AMOLED panel runs almost edge to edge, so the ultra-narrow bezel dresses down the case further - there's more screen than frame at a glance, which is exactly the illusion a 46mm watch needs. And for anyone who takes it off at the sink or in the shower without thinking twice, it's rated water-resistant to 50 metres, so that's one less thing to plan around.
What was actually running while the clock counted down
21 days is meaningless without knowing what the watch was actually doing for 21 days, so here's the load: animated wallpaper running the whole time, sleep tracking on most nights, notifications pushed through for WhatsApp and calls, daily health tracking active, weather forecast syncing, and continuous heart rate monitoring. That's a realistic daily-driver setup, not a lab-conditions best case with everything switched off.
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Under that load, the watch was still alive and reporting on Day 21, with 13% left before it needed a plug. That's about as close to "does exactly what it says on the box" as a wearable battery claim gets.
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"It detects stress and runs a health check in the time it takes to glance at your wrist - that's the part I didn't expect to use daily."
150 sport modes is overkill until it isn't
150 sport modes sounds like a marketing number until you're switching between walking, a jump-heavy HIIT session and the treadmill in the same week and the watch already has a preset for each - auto-detecting the activity type reasonably well even when I forgot to select a mode manually.
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The health layer runs quietly underneath all of that: sleep tracking, step counting, stress tracking and SpO2 measurement, all logged without needing to be told to. Stress tracking in particular turned out more useful than expected - a quick tap gives a basic health read that's fast enough to actually become a habit, not a feature you check once and forget.
I can't verify hardware internals myself, but Xiaomi credits the readings to a new sensor module - four LEDs paired with four photodiodes, versus the single sensor most trackers get by with. Whatever's actually driving it, the heart rate and blood oxygen numbers held up consistently enough across the three weeks that I stopped double-checking them against anything else.
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Its own OS, its own rules
Worth knowing upfront: this doesn't run Wear OS, so don't go looking for it on the Google Play Store - it runs Xiaomi's own HyperOS 3, paired through Xiaomi's own app instead. Pairing itself was a non-event, which is exactly what pairing should be: open the app, watch finds itself, done.
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The watch face library is deeper than I expected, and a handful of the faces are doing real work for the premium feel - the right face makes the S5 look like a considerably more expensive watch. Small touch I liked: picking a face flags how much battery it'll cost you before you commit, so you're not finding out the hard way on Day 15.
One more detail worth a mention for anyone who takes it off at a gym or leaves it on a desk: it can be locked with a PIN whenever it's off the wrist.
Does what the box says, wears better than expected
The headline claim held up under a realistic daily load, which is the bar that matters most for a watch like this - and the 46mm case never once felt like the compromise that number usually implies. Between the leather strap, the watch-face polish and the battery-conscious touches in the app, this reads like Xiaomi aiming a notch above where the S-series has typically sat.
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