Xiaomi claims 15 days of battery life for the Watch S4, five-system dual-band GNSS and a screen that peaks at 2,200 nits, all from 120 euros at most retailers. On paper, that is enough to worry some well-established names. Three independent tests, run on both sizes of the watch, tell a different story: the screen and the heart rate sensor deliver, but real battery life drops to 3 to 5 days depending on use, and GPS accuracy splits the testers themselves.
© Xiaomi, official photo used for editorial purposes
Xiaomi, the missing name in the RunMorph GPS watch lineup
The GPS running watch market in France is still dominated by a tight core of specialist brands: Garmin, Coros, Polar and Suunto up front, with Amazfit and Huawei as outsiders in the affordable segment. Xiaomi, despite being one of the biggest sellers of smartphones and connected devices in France, has stayed largely absent from the sport-oriented smartwatch segment, even with a Watch S range that has been around for several generations.
The Watch S4, launched in March 2025 at Mobile World Congress in Barcelona and still widely sold in France in autumn 2026, sums up that position well: a list price of 169.99 euros that regularly drops below 130 euros at retailers, one of the brightest screens on the market across all brands, but a clear positioning as a general-purpose smartwatch rather than a structured training tool. At RunMorph, we come at it with the question that matters to a runner: beyond the impressive spec sheet, what is it actually worth for running?
Xiaomi Watch S4: what the brand claims vs what testers measure
On the screen and the heart rate sensor, Xiaomi's numbers hold up: the three independent testers we looked at all confirm a very bright panel and reliable heart rate readings. It is on battery life, the most heavily marketed selling point, that the gap with real-world use is widest.
| Data point | Claimed by Xiaomi | Measured by independent testers |
|---|
| Heart rate accuracy | Up to 98% according to Xiaomi's in-house labs | Confirmed by one tester who compared it with an Apple Watch Ultra, only 1 to 2 beats apart |
| Screen brightness | 1,500 nits HBM, 2,200 nits peak | Confirmed, readability rated excellent in direct sunlight by all 3 testers |
| Battery life | 15 days in standard use | Between 3 and 8 days depending on the tester and settings (Always-On Display in particular), up to 5 times less than claimed |
| GPS accuracy | 5-system dual-band GNSS, positioning billed as fast and accurate | Mixed verdicts: 2 testers out of 3 find the track shaky in the city, the 3rd measures consistent distances with no signal loss |
The claimed 15 days rest on a specific protocol published by Xiaomi itself: sleep, breathing, stress and SpO2 tracking switched off, Always-On Display off, a single manual sync per day. In other words, minimal use that matches none of the three real test profiles reviewed for this article.
Dual-band GPS: why the verdicts differ so much
A tester from the French site PhonAndroid, who compared the Watch S4 with an Apple Watch Ultra worn at the same time, describes a track that is "hesitant and not really linear", adding a few metres never actually run to the total distance. The reviewer at Journal du Geek, on the compact 41 mm version, reaches a similar conclusion: in open terrain the track stays correct, but in dense urban areas the lock is slower and distance gaps appear, with accuracy rated below the latest Garmin, Suunto or Coros generations.
On the other hand, a watch specialist from the site Le Petit Gousset, on the same 41 mm version, reports clean tracks, consistent distances and rare connection drops. This split, two critical verdicts against one favourable one on a GNSS that is identical on paper (dual-band L1+L5, 5 constellations), points to a higher sensitivity than usual to test conditions: route type, cloud cover, urban density. At RunMorph, our takeaway is that none of the three testers reports accuracy on par with the best on the market, but how much it actually bothers you clearly depends a lot on where you run.
© Xiaomi, official photo used for editorial purposes
A closed ecosystem that holds runners back
The Watch S4 runs HyperOS 2, Xiaomi's own system, not Wear OS. The direct consequence, flagged by all 3 testers: no app store, so no way to install Strava, Komoot or a music streaming app directly on the watch. A sync bridge exists between Mi Fitness and Strava to pull your data afterwards, but nothing like the native connection offered by Garmin or Coros.
On iOS, the experience gets worse: no replying to texts, no real-time location sharing, contactless payment can't be set up. And on NFC, Xiaomi's promise of worldwide Visa and Mastercard compatibility had not, at the time of writing, translated into a single French bank confirmed as compatible by the testers we reviewed: check this before buying if it is part of your reasoning.
Fit on the wrist: two very different sizes
Unlike most sports watches, Xiaomi does not offer a dedicated women's version of the standard 47.3 mm model, which the PhonAndroid tester found bulky on small wrists. The brand makes up for it with a second size, the Watch S4 41 mm: stainless steel case, 9.5 mm thick, 32 g without strap, 1.32-inch AMOLED screen. This more compact version even adds a skin temperature sensor missing from the standard model, useful for menstrual cycle prediction, but its measured real battery life (3 to 5 days according to the 2 testers of the 41 mm version) is clearly shorter than that of the 47.3 mm model tested by PhonAndroid, which fits with its smaller battery.
Xiaomi Watch S4 vs Watch S3: what really changes
| Criterion | Watch S3 | Watch S4 |
|---|
| Screen brightness | 600 nits | 1,500 nits HBM / 2,200 nits peak (x2.5) |
| Navigation | Push button only | Rotating crown added |
| Launch price | About 150 € | 169.99 € (+20 €) |
| Customisation | Interchangeable bezels/straps, kits between 9.99 € and 39.99 € | Same system, kits standardised at 19.99 € each |
The short version: the S4 makes clear progress on the screen and on ergonomics with its rotating crown, two points every tester confirms. An S3 owner happy with their battery life has no urgent reason to upgrade, since the GPS and battery architecture stays close. If you use your watch in full sun or like physical navigation, though, you have a real reason to switch.
Xiaomi Watch S4 vs Amazfit Active Max and Garmin Forerunner 55: the comparison
| Criterion | Xiaomi Watch S4 | Amazfit Active Max | Garmin Forerunner 55 |
|---|
| Price | 120-170 € | 169.90 € | 159 € |
| Screen | 1.43" AMOLED, 2,200 nits peak | AMOLED, 3,000 nits | Transflective, no always-on backlight |
| GPS | Dual-band, accuracy rated average | GPS accuracy also criticised by the press | Single-band but proven reliability |
| Running ecosystem | Closed, no structured plans | Maps available, Zepp ecosystem | Training Status, full Garmin Connect |
| Positioning | General smartwatch with sports features | Outdoor watch with maps | Dedicated, minimalist running watch |
The short version: the Amazfit Active Max shares a similar weak spot with the Watch S4, GPS accuracy that the specialist press also calls out despite an even brighter screen, which suggests a fairly common compromise in this price bracket. A runner who mainly wants a spectacular screen for broad smartwatch use can be happy with the Xiaomi or the Amazfit. If you mainly want to run with reliable data and real progress tracking, look instead at a Garmin Forerunner 55: plainer to look at, but built around GPS and an ecosystem designed for running.
Everyday health and sports tracking: what actually works
Beyond running, all 3 testers praise complete health tracking for the price: SpO2, stress, sleep with a guided 21-day improvement programme from Xiaomi, and more than 150 sport modes covering swimming, cycling, strength training and skiing, the latter with dedicated fall detection. The Sport Vlog feature, which remotely triggers video recording on your smartphone with your data overlaid on screen, is an original touch praised by Journal du Geek, even if it stays a gimmick for a typical runner.
Our field verdict: who is it for, and with which training plan?
The Watch S4 makes sense for a casual runner who wants to keep an eye on heart rate and runs without investing in a dedicated watch, or for someone who puts everyday use (notifications, screen, all-day battery) ahead of pure sports performance. For a runner who builds their training around a time goal, the lack of advanced training tools and the limited real battery life weigh heavily.
Pair it with a RunMorph plan
With no structured training plans built into the watch, a runner using a Watch S4 is better off following their sessions with our RunMorph training plans alongside it, using the watch only to measure heart rate and distance rather than to steer the session itself.
RunMorph Coach verdict
The Xiaomi Watch S4 keeps part of its promise: the screen and the heart rate sensor really do perform as advertised, at a price that remains unbeatable in this segment. But Xiaomi's headline argument, 15 days of battery life, does not survive normal use according to the 3 testers we reviewed, and GPS accuracy doesn't even reach consensus among them.
RunMorph score: 6.4/10. The weighting puts more emphasis on GPS reliability, real battery life and the running ecosystem than on the screen and design, even though those are its least disputed strengths: this gap between the marketing pitch and actual use by runners explains a score below the more generous mainstream reviews.
Xiaomi Watch S4 FAQ
What real battery life can you expect from the Xiaomi Watch S4?
Between 3 and 8 days according to the 3 testers we reviewed and the settings enabled, far from the 15 days claimed by Xiaomi, which rely on minimal use (continuous health tracking off, Always-On screen off).
Is the Xiaomi Watch S4 reliable for running in the city?
Verdicts are mixed: 2 testers out of 3 report a shaky track and distance gaps in dense urban areas, while a 3rd tester measures consistent distances. None of the three rates it on par with the best Garmin, Suunto or Coros models.
Can you install Strava directly on the Xiaomi Watch S4?
No: HyperOS 2 has no app store. Data can be synced from Mi Fitness to Strava afterwards, but there is no native connection during the activity.
How much does the Xiaomi Watch S4 cost in France?
169.99 € at the official price, but commonly found between 120 and 150 € at most retailers in autumn 2026.
Is there a smaller version for slim wrists?
Yes, the Watch S4 41 mm: 32 g steel case, 1.32-inch screen, with an extra skin temperature sensor, but real battery life measured at 3-5 days by 2 testers, shorter than the 47.3 mm model.