Where they actually differ
The most decisive specs, ranked by how much they matter — before the full spec table.
| Spec | Apple - Watch Ultra 2 | Xiaomi - Watch S4 |
|---|---|---|
| Battery life | 36 h | 360 h |
| Peak brightness | 3000 nits | 2200 nits |
| Display size | 1.92 " | 1.43 " |
| Weight | 61.4 g | 44 g |
| Water resistance | 10 ATM | 5 ATM |
Between the Watch Ultra 2 and Watch S4, the Watch Ultra 2 comes out ahead in peak brightness / display size, while the Watch S4 wins on battery life / weight. Overall, the Watch Ultra 2 scores 71.9 and the Watch S4 scores 76.3 on our Mars Score.
Which should you buy?
The Watch S4 edges ahead on the Mars Score (71.9 vs 76.3), but the 4.4-point gap is small enough that the right pick comes down to which spec advantages matter to you.
Pick the Watch Ultra 2 if the display is what you stare at all day — refresh rate, brightness, or sharpness is where the difference will be most visible. The biggest gaps in its favor are peak brightness, display size, water resistance. The single most decisive one: Peak brightness — 36.36% more. 3000 nits vs 2200 nits.
Pick the Watch S4 if your top frustration with your current device is running out of charge before the day ends — endurance is the lead spec here. Its strongest claims are battery life, weight. The single most decisive one: Battery life — 900.00% more. 360 h vs 36 h.
Both ship with comparable ecg, cellular, spo2, so those specs do not separate the two — focus on the differences below.
Bottom line: there is no wrong answer here — match the spec advantages to how you actually use the product. The Mars Score parity says both are well-rounded; the differences are about trade-offs, not quality.
Which should you buy: Apple - Watch Ultra 2 or Xiaomi - Watch S4?
Xiaomi - Watch S4 leads the current Mars Score by 4.4 points.The more useful decision is the trade-off behind that result: compare display size, battery life against the way you will actually use the product.
Choose Apple - Watch Ultra 2 if…
Apple - Watch Ultra 2 has the measurable edge on peak brightness nits, display size in, water resistance atm.
Choose Xiaomi - Watch S4 if…
Xiaomi - Watch S4 has the measurable edge on battery life h, weight g.
This is a structured comparison of the published catalog values. It is not a claim of identical real-world performance across every workload; use the linked spec drill-downs and methodology page to inspect the inputs.
Why Apple - Watch Ultra 2 wins
- ▲Peak brightness — 36.36% more. 3000 nits vs 2200 nits.
- ▲Display size — 34.27% more. 1.92 " vs 1.43 ".
- ▲Water resistance — 5.00 ATM more. 10 vs 5.
Why Xiaomi - Watch S4 wins
- ▲Battery life — 900.00% more. 360 h vs 36 h.
- ▲Weight — 17.40 g less. 44 vs 61.4.
Spec comparison
Design
| Spec | Apple - Watch Ultra 2 | Xiaomi - Watch S4 |
|---|---|---|
| Case size | 49 mmlead | 47 mm |
| Weight | 61.4 g | 44 glead |
| Case material | titanium | stainless steel |
| Water resistanceⓘ | 10 ATMlead | 5 ATM |
Display
| Spec | Apple - Watch Ultra 2 | Xiaomi - Watch S4 |
|---|---|---|
| Display size | 1.92 "lead | 1.43 " |
| Always-on display | true | true |
| Peak brightnessⓘ | 3000 nitslead | 2200 nits |
Health & Fitness
| Spec | Apple - Watch Ultra 2 | Xiaomi - Watch S4 |
|---|---|---|
| ECG | true | true |
| SpO2 | true | true |
| Temperature sensor | true | true |
| Sleep tracking | true | true |
| Blood pressure | false | false |
Battery & Connectivity
| Spec | Apple - Watch Ultra 2 | Xiaomi - Watch S4 |
|---|---|---|
| Battery lifeⓘ | 36 h | 360 hlead |
| GPS | true | true |
| Cellular | true | true |
| NFC | true | true |
| OS | watchOS | HyperOSlead |
Frequently asked
Which has longer battery life, Watch Ultra 2 or Watch S4?+
Watch S4 lasts 360 hours vs 36 hours.
Do Watch Ultra 2 or Watch S4 support ECG?+
Both support ECG.
Which has cellular, Watch Ultra 2 or Watch S4?+
Both offer cellular variants.